diff --git a/src/main/java/learnrxjava/ComposableListExercises.java b/src/main/java/learnrxjava/ComposableListExercises.java
index a13940c..193b36a 100644
--- a/src/main/java/learnrxjava/ComposableListExercises.java
+++ b/src/main/java/learnrxjava/ComposableListExercises.java
@@ -127,11 +127,11 @@ public <R> ComposableList<R> map(Function<T, R> projectionFunction) {
             // Note that you can apply a projectionFunction to a value like this:
             //  projectionFunction.apply(5)
             // ------------ INSERT CODE HERE! ----------------------------
-            
+            results.add(projectionFunction.apply(itemInList));
         });
         
-        //return results;
-        throw new UnsupportedOperationException("Not implemented yet.");
+        return results;
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
     
     /*
@@ -146,10 +146,10 @@ public static ComposableList<JSON> exercise5() {
             new Video(654356453, "Bad Boys", 5.0),
             new Video(65432445, "The Chamber", 4.0),
             new Video(675465, "Fracture", 5.0));
-         
-        // complete this expression 
-        // return newReleases.map(video -> 
-        throw new UnsupportedOperationException("Not implemented yet.");
+
+        // complete this expression
+         return newReleases.map(video -> json("id", video.id, "title", video.title));
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
 
     /*
@@ -189,11 +189,13 @@ public static ComposableList<Video> exercise6() {
         newReleases.forEach(video -> {
             // Insert code here that adds a video to the highRatedVideos list
             // if it has a rating of 5.0.
-
+            if (video.rating == 5.0) {
+                highRatedVideos.add(video);
+            }
         });
         
-        // return highRatedVideos;
-        throw new UnsupportedOperationException("Not implemented yet.");        
+         return highRatedVideos;
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
     
     /*
@@ -221,11 +223,13 @@ public ComposableList<T> filter(Predicate<T> predicateFunction) {
             // Note: you can apply the predicateFunction to a value like this:
             // predicateFunction.test(5)
             // ------------ INSERT CODE HERE! ----------------------------
-
+            if (predicateFunction.test(itemInList)) {
+                results.add(itemInList);
+            }
         });
 
-        // return results;
-        throw new UnsupportedOperationException("Not implemented yet.");
+         return results;
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
 
     /*
@@ -266,7 +270,9 @@ public static ComposableList<Integer> exercise8() {
         // ------------ INSERT CODE HERE! -----------------------------------
         //return newReleases // Complete this expression
 
-        throw new UnsupportedOperationException("Not implemented yet.");
+        return newReleases.filter(video -> video.rating == 5.0).map(video -> video.id);
+
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
 
     /*
@@ -299,9 +305,12 @@ public static ComposableList<Integer> exercise9() {
         // ------------   INSERT CODE HERE!  -----------------------------------
         // Use two nested forEach loops to flatten the movieLists into a list of
         // video ids.
+        movieLists.forEach(list -> {
+            list.videos.forEach(video -> allVideoIdsInMovieLists.add(video.id));
+        });
         // ------------   INSERT CODE HERE!  -----------------------------------
-        //return allVideoIdsInMovieLists;
-        throw new UnsupportedOperationException("Not implemented yet.");
+        return allVideoIdsInMovieLists;
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
     
     /*
@@ -338,11 +347,11 @@ public <R> ComposableList<R> concatMap(
             // Note that you can apply a projectionFunction to a value like this:
             // projectionFunctionThatReturnsList.apply(5)
             // ------------ INSERT CODE HERE! ----------------------------
-
+            projectionFunctionThatReturnsList.apply(itemInList).forEach(results::add);
         }
         
-        //return results;
-        throw new UnsupportedOperationException("Not implemented yet.");
+        return results;
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
     
     /*
@@ -371,12 +380,14 @@ public static ComposableList<Integer> exercise11() {
         // Use map and concatAll to flatten the movieLists in a list of video ids.
         // return movieLists // finish expression
         // ------------   INSERT CODE HERE!  -----------------------------------
+        return movieLists.concatMap(movieList -> movieList.videos.map(video -> video.id));
+
         // **************ANSWER START***************//
         // return movieLists.
         //     concatMap(movieList -> 
         //         movieList.videos.map(video -> video.id));
         // **************ANSWER END***************//
-        throw new UnsupportedOperationException("Not implemented yet.");
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
     
     /*
@@ -449,8 +460,12 @@ public static ComposableList<JSON> exercise12() {
         //   {"id": 675465,"title": "Fracture","boxart":"http://cdn-0.nflximg.com/images/2891/Fracture150.jpg" },
         // };
 
-        // return movieLists // Complete this expression!
-        throw new UnsupportedOperationException("Not implemented yet.");
+        return movieLists.concatMap(movieList ->
+                movieList.videos.concatMap(video ->
+                        video.boxarts.filter(boxArt -> boxArt.width == 150 && boxArt.height == 200)
+                                .map((BoxArt filtered) -> json("id", video.id, "title", video.title, "boxart", filtered.url))));
+
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
 
     /*
@@ -486,11 +501,13 @@ public static BoxArt exercise13() {
                     // ****** INSERT CODE HERE ********
                     // Assign the largestBoxart to the current boxart, and assign the maxSize to the currentSize.
                     // ****** INSERT CODE HERE ********
+                    largestBoxart = boxart;
+                    maxSize = currentSize;
                 }
             }
 
-        // return largestBoxart;
-        throw new UnsupportedOperationException("Not implemented yet.");
+         return largestBoxart;
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
     /*
     Exercise 14: Implement reduce()
@@ -520,6 +537,7 @@ public ComposableList<T> reduce(BiFunction<T, T, T> combiner) {
             // ************ INSERT CODE HERE **************
             //  if the list is empty, return this
             // ********************************************
+            return this;
         } else {
             accumulatedValue = this.get(0);
 
@@ -531,14 +549,14 @@ public ComposableList<T> reduce(BiFunction<T, T, T> combiner) {
                 // Set accumulatedValue to the result of passing accumulatedValue and the list value at the 
                 // counter index to the combiner function.
                 // ****** INSERT CODE HERE ********
-
+                accumulatedValue = combiner.apply(accumulatedValue, this.get(counter));
                 counter++;
             }
 
-            //return ComposableListExercises.of(accumulatedValue);
+            return ComposableListExercises.of(accumulatedValue);
         }
 
-        throw new UnsupportedOperationException("Not implemented yet.");
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
 
     /*
@@ -568,7 +586,7 @@ public <R> ComposableList<R> reduce(R initialValue, BiFunction<R, T, R> combiner
 
         // If the list is empty, do nothing
         if (this.size() == 0) {
-            return new ComposableListExercises<R>();
+            return new ComposableListExercises<>();
         } else {
             counter = 0;
             accumulatedValue = initialValue;
@@ -596,10 +614,12 @@ public static ComposableList<Integer> exercise16() {
         // returns a list with one item.
 
         // complete the expression below
-        //return ratings.reduce
+        return ratings.reduce(ratings.get(0), (acc, curr) -> curr > acc ? curr : acc);
 
-        throw new UnsupportedOperationException("Not implemented yet.");
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
+
+    static Function<BoxArt, Integer> size = boxArt -> boxArt.width * boxArt.height;
     /*
     Exercise 17: Retrieve url of the largest boxart
 
@@ -616,8 +636,10 @@ public static ComposableList<String> exercise17() {
 
         // You should return a list containing only the largest box art. Remember that reduce always
         // returns a list with one item.
-        // return boxarts.reduce  
-        throw new UnsupportedOperationException("Not implemented yet.");
+        return boxarts.reduce(boxarts.get(0), (acc, curr) -> size.apply(curr) > size.apply(acc) ? curr : acc)
+                .map(boxArt -> boxArt.url);
+
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
 
     /*
@@ -666,7 +688,7 @@ public static ComposableList<Map<Integer, String>> exercise18() {
             reduce(
             // Use an empty map as the initial value instead of the first item in
             // the list.
-            new HashMap<Integer, String> (),
+            new HashMap<>(),
             (accumulatedMap, video) -> {
                 // ************ INSERT CODE HERE ************
                 // Remember that you the functions passed to map, filter, concatMap, reduce, and zip can only 
@@ -677,7 +699,11 @@ public static ComposableList<Map<Integer, String>> exercise18() {
                 // exercise simply copy the accumulatedMap into a new map, add the video information to the copy, 
                 // and return the copy.
                 // ************ INSERT CODE HERE ************
-                throw new UnsupportedOperationException("Not implemented yet.");
+                HashMap<Integer, String> newMap = new HashMap<>();
+                newMap.putAll(accumulatedMap);
+                newMap.put(video.id, video.title);
+                return newMap;
+//                throw new UnsupportedOperationException("Not implemented yet.");
             });
     }
 
@@ -750,15 +776,15 @@ public static ComposableList<JSON> exercise19() {
         // ];
 
         // Uncomment the code below and finish the expression.
-        /*
-        return movieLists.
-            concatMap(movieList -> {
-
-            })
-         */
-        throw new UnsupportedOperationException("Not implemented yet.");
+        return movieLists.concatMap(movieList ->
+                movieList.videos.concatMap(video ->
+                        video.boxarts.reduce(video.boxarts.get(0), minSize).map(boxArt ->
+                                json("id", video.id, "title", video.title, "boxart", boxArt.url))));
     }
 
+    static BiFunction<BoxArt, BoxArt, BoxArt> minSize = (left, right) ->
+            size.apply(left) < size.apply(right) ? left : right;
+
     /*
     Exercise 20: Zipping Lists
 
@@ -805,10 +831,12 @@ public static ComposableList<JSON> exercise20() {
         for (int counter = 0; counter < Math.min(videos.size(), bookmarks.size()); counter++) {
             // Insert code here to create a {"videoId" : videoId, "bookmarkId" : bookmarkId} JSON 
             // using json() and add it to the videoIdAndBookmarkIdPairs list.
+            videoIdAndBookmarkIdPairs.add(
+                    json("videoId", videos.get(counter).id, "bookmarkId", bookmarks.get(counter).id));
         }
 
-        // return videoIdAndBookmarkIdPairs;
-        throw new UnsupportedOperationException("Not implemented yet.");
+         return videoIdAndBookmarkIdPairs;
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
 
     /*
@@ -825,16 +853,18 @@ public static ComposableList<JSON> exercise20() {
         ComposableList.of(4,5,6), 
         (x,y) -> x + y) is structurally equivalent to ComposableList.of(5,7,9)
      */
-    public static <T0,T1,R> ComposableList<R> zip(ComposableList<T0> left, ComposableList<T1> right, BiFunction<T0,T1, R> combinerFunction) {
+    public static <T0,T1,R> ComposableList<R> zip(ComposableList<T0> left, ComposableList<T1> right, BiFunction<T0, T1,
+            R> combiner) {
         ComposableListExercises<R> results = new ComposableListExercises<R>();
 
         for (int counter = 0; counter < Math.min(left.size(), right.size()); counter++) {
             // Add code here to apply the combinerFunction to the left and right-hand items in the 
             // respective lists, and add the result to the results List
+            results.add(combiner.apply(left.get(counter), right.get(counter)));
         }
 
-        // return results;
-        throw new UnsupportedOperationException("Not implemented yet.");
+         return results;
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
 
     /*
@@ -875,8 +905,9 @@ public static ComposableList<JSON> exercise22() {
         );
 
         //... finish this expression
-        // return ComposableListExercises.zip( 
-        throw new UnsupportedOperationException("Not implemented yet.");
+         return ComposableListExercises.zip(videos, bookmarks, ((video, bookmark) ->
+                 json("videoId", video.id, "bookmarkId", bookmark.id)));
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
 
     /*
@@ -962,15 +993,22 @@ public static ComposableList<JSON> exercise23() {
             )
         );
 
-        //------------ COMPLETE THIS EXPRESSION --------------
-        /*
-        return movieLists.
-            concatMap(movieList -> {
+        Function<ComposableList<BoxArt>, ComposableList<BoxArt>> reduceSmallest = boxArts ->
+                boxArts.reduce(boxArts.get(0), minSize);
 
-            });
-        */
+        Predicate<InterestingMoment> isMiddle = interestingMoment -> interestingMoment.type.equals("Middle");
 
-        throw new UnsupportedOperationException("Not implemented yet.");
+        //------------ COMPLETE THIS EXPRESSION --------------
+        return movieLists.
+            concatMap(movieList ->
+                    movieList.videos.concatMap(video ->
+                            zip(reduceSmallest.apply(video.boxarts), video.interestingMoments.filter(isMiddle),
+                                    (boxArt, moment) ->
+                                            json("id", video.id, "title", video.title, "time", moment.time, "url",
+                                                    boxArt.url)
+                            )));
+
+//        throw new UnsupportedOperationException("Not implemented yet.");
     }
 
 
diff --git a/src/main/java/learnrxjava/ObservableExercises.java b/src/main/java/learnrxjava/ObservableExercises.java
index a7c5d00..4681591 100644
--- a/src/main/java/learnrxjava/ObservableExercises.java
+++ b/src/main/java/learnrxjava/ObservableExercises.java
@@ -1,5 +1,9 @@
 package learnrxjava;
 
+import java.util.function.BiFunction;
+import java.util.function.Function;
+
+import learnrxjava.types.BoxArt;
 import learnrxjava.types.JSON;
 import learnrxjava.types.Movies;
 import rx.Observable;
@@ -12,7 +16,8 @@ public class ObservableExercises {
      * @return "Hello World!"
      */
     public Observable<String> exerciseHello() {
-        return Observable.error(new RuntimeException("Not Implemented"));
+//        return Observable.error(new RuntimeException("Not Implemented"));
+        return Observable.just("Hello World!");
     }
 
     /**
@@ -21,7 +26,8 @@ public Observable<String> exerciseHello() {
      * @param "Hello Name!"
      */
     public Observable<String> exerciseMap(Observable<String> hello) {
-        return Observable.error(new RuntimeException("Not Implemented"));
+//        return Observable.error(new RuntimeException("Not Implemented"));
+        return hello.map(name -> "Hello " + name);
     }
 
     /**
@@ -32,7 +38,8 @@ public Observable<String> exerciseMap(Observable<String> hello) {
      * 6-Even
      */
     public Observable<String> exerciseFilterMap(Observable<Integer> nums) {
-        return Observable.error(new RuntimeException("Not Implemented"));
+//        return Observable.error(new RuntimeException("Not Implemented"));
+        return nums.filter(num -> num % 2 == 0).map(num -> num + "-Even");
     }
 
     /**
@@ -42,7 +49,9 @@ public Observable<String> exerciseFilterMap(Observable<Integer> nums) {
      * @return Observable of Integers of Movies.videos.id
      */
     public Observable<Integer> exerciseConcatMap(Observable<Movies> movies) {
-        return Observable.error(new RuntimeException("Not Implemented"));
+//        return Observable.error(new RuntimeException("Not Implemented"));
+        return movies.concatMap(m -> m.videos.map(video -> video.id));
+//        return movies.flatMap(movies1 -> movies1.videos).concatMap(movie -> Integer.valueOf(movie.id));
     }
 
     /**
@@ -59,7 +68,8 @@ public Observable<Integer> exerciseConcatMap(Observable<Movies> movies) {
      * @return Observable of Integers of Movies.videos.id
      */
     public Observable<Integer> exerciseFlatMap(Observable<Movies> movies) {
-        return Observable.error(new RuntimeException("Not Implemented"));
+//        return Observable.error(new RuntimeException("Not Implemented"));
+        return movies.flatMap(movies1 -> movies1.videos).map(movie -> movie.id);
     }
 
     /**
@@ -68,7 +78,8 @@ public Observable<Integer> exerciseFlatMap(Observable<Movies> movies) {
      * Use reduce to select the maximum value in a list of numbers.
      */
     public Observable<Integer> exerciseReduce(Observable<Integer> nums) {
-        return Observable.error(new RuntimeException("Not Implemented"));
+//        return Observable.error(new RuntimeException("Not Implemented"));
+        return nums.reduce(Math::max);
     }
 
     /**
@@ -83,7 +94,14 @@ public Observable<Integer> exerciseReduce(Observable<Integer> nums) {
      * See Exercise 19 of ComposableListExercises
      */
     public Observable<JSON> exerciseMovie(Observable<Movies> movies) {
-        return Observable.error(new RuntimeException("Not Implemented"));
+//        return Observable.error(new RuntimeException("Not Implemented"));
+
+        Function<BoxArt, Integer> size = boxArt -> boxArt.width * boxArt.height;
+
+        return movies.flatMap(movies1 ->
+                movies1.videos.flatMap(movie ->
+                        movie.boxarts.reduce((left, right) -> size.apply(left) < size.apply(right) ? left : right)
+                                .map(boxArt -> json("id", movie.id, "title", movie.title, "boxart", boxArt.url))));
     }
 
     /**
@@ -94,7 +112,8 @@ public Observable<JSON> exerciseMovie(Observable<Movies> movies) {
      * output -> "one fish", "two fish", "red fish", "blue fish"
      */
     public Observable<String> exerciseZip(Observable<String> a, Observable<String> b) {
-        return Observable.error(new RuntimeException("Not Implemented"));
+//        return Observable.error(new RuntimeException("Not Implemented"));
+        return Observable.zip(a, b, (s1, s2) -> s1 + " " + s2);
     }
 
     /**
@@ -102,7 +121,8 @@ public Observable<String> exerciseZip(Observable<String> a, Observable<String> b
      * and replace it with "default-value".
      */
     public Observable<String> handleError(Observable<String> data) {
-        return Observable.error(new RuntimeException("Not Implemented"));
+//        return Observable.error(new RuntimeException("Not Implemented"));
+        return data.onErrorResumeNext(s -> Observable.just("default-value"));
     }
 
     /**
@@ -110,7 +130,8 @@ public Observable<String> handleError(Observable<String> data) {
      * with retry capability.
      */
     public Observable<String> retry(Observable<String> data) {
-        return Observable.error(new RuntimeException("Not Implemented"));
+//        return Observable.error(new RuntimeException("Not Implemented"));
+        return data.retry();
     }
 
     // This function can be used to build JSON objects within an expression
diff --git a/src/main/java/learnrxjava/types/ComposableList.java b/src/main/java/learnrxjava/types/ComposableList.java
index ab2df88..a3680b5 100644
--- a/src/main/java/learnrxjava/types/ComposableList.java
+++ b/src/main/java/learnrxjava/types/ComposableList.java
@@ -7,19 +7,21 @@
 
 public interface ComposableList<T> extends Iterable<T> {
 
-    public <R> ComposableList<R> map(Function<T, R> projectionFunction);
+    <R> ComposableList<R> map(Function<T, R> projectionFunction);
 
-    public ComposableList<T> filter(Predicate<T> predicateFunction);
+    ComposableList<T> filter(Predicate<T> predicateFunction);
 
-    public <R> ComposableList<R> concatMap(Function<T, ComposableList<R>> projectionFunctionThatReturnsList);
+    <R> ComposableList<R> concatMap(Function<T, ComposableList<R>> projectionFunctionThatReturnsList);
 
-    public ComposableList<T> reduce(BiFunction<T, T, T> combiner);
+    ComposableList<T> reduce(BiFunction<T, T, T> combiner);
 
-    public <R> ComposableList<R> reduce(R initialValue, BiFunction<R, T, R> combiner);
+    <R> ComposableList<R> reduce(R initialValue, BiFunction<R, T, R> combiner);
 
-    public int size();
+//    <T0,T1,R> ComposableList<R> zip(ComposableList<T0> left, ComposableList<T1> right, BiFunction<T0, T1, R> combiner);
 
-    public void forEach(Consumer<? super T> action);
+    int size();
 
-    public T get(int index);
+    void forEach(Consumer<? super T> action);
+
+    T get(int index);
 }