diff --git a/index.js b/index.js
index f61169392..bf50c21e9 100644
--- a/index.js
+++ b/index.js
@@ -48,8 +48,8 @@ function processFirstItem(stringList, callback) {
  * [2] Invoking `processLength` passing `[]` and `(num) => "There are " + num`,
  * should return "There are 0".
 */
-function processLength(/* CODE HERE */) {
-  /* CODE HERE */
+function processLength(list, callback) {
+  return callback(list.length);
 }
 
 /**
@@ -66,8 +66,8 @@ function processLength(/* CODE HERE */) {
  * Invoking `processLastItem` passing `['foo', 'bar']` and `(str) => str + str`,
  * should return 'barbar'.
 */
-function processLastItem(/* CODE HERE */) {
-  /* CODE HERE */
+function processLastItem(stringList, callback) {
+  return callback(stringList[stringList.length - 1]);
 }
 
 /**
@@ -88,8 +88,8 @@ function processLastItem(/* CODE HERE */) {
  * [2] Invoking `processSum` passing `-5`, '-1', and `(num) => num + 1000`,
  * should return 994.
 */
-function processSum(/* CODE HERE */) {
-  /* CODE HERE */
+function processSum(num1, num2, callback) {
+  return callback(num1 + num2);
 }
 
 /**
@@ -110,8 +110,8 @@ function processSum(/* CODE HERE */) {
  * [2] Invoking `processProduct` passing 25 and 0 and `(num) => num + 1000`,
  * should return 1000.
 */
-function processProduct(/* CODE HERE */) {
-  /* CODE HERE */
+function processProduct(num1, num2, callback) {
+  return callback(num1 * num2);
 }
 
 /**
@@ -132,8 +132,9 @@ function processProduct(/* CODE HERE */) {
  * [2] Invoking `processDuplicateFree` passing `[1,1,2,2,3]` and `(arr) => arr.length`,
  * should return 3.
 */
-function processDuplicateFree(/* CODE HERE ONLY AFTER COMPLETING ALL OTHER TASKS */) {
-  /* CODE HERE ONLY AFTER COMPLETING ALL OTHER TASKS */
+function processDuplicateFree(list, callback) {
+  let DupeFreeSet = new Set(list);
+  return callback(Array.from(DupeFreeSet));
 }
 
 /////////////// HIGHER-ORDER ARRAY METHODS ///////////////
@@ -155,8 +156,10 @@ function processDuplicateFree(/* CODE HERE ONLY AFTER COMPLETING ALL OTHER TASKS
  * 
  * [2] Invoking `lowerCaseStrings` with `['a', 'b', 'c' ]` will return `[ 'a', 'b', 'c' ]`.
 */
-function lowerCaseStrings(/* code here */) {
-  /* code here */
+function lowerCaseStrings(strings) {
+  let LCstrings = [];
+  strings.forEach(strings => { LCstrings.push(strings.toLowerCase()) });
+  return LCstrings;
 }
 
 /**
@@ -174,8 +177,8 @@ function lowerCaseStrings(/* code here */) {
  * 
  * [2] Invoking `isItAnApple` with `['a', 'b', 'c' ]` will return `[ false, false, false ]`.
 */
-function isItAnApple(/* code here */) {
-  /* code here */
+function isItAnApple(strings) {
+  return strings.map(strings => (strings === 'apple') ? true : false);
 }
 
 /**
@@ -194,8 +197,8 @@ function isItAnApple(/* code here */) {
  * 
  * [2] Invoking `removeApple` with `['a', 'b', 'c' ]` will return `[ 'a', 'b', 'c' ]`.
 */
-function removeApple(/* code here */) {
-  /* code here */
+function removeApple(strings) {
+  return strings.filter(strings => strings != 'apple');
 }
 
 /**
@@ -213,8 +216,8 @@ function removeApple(/* code here */) {
  * 
  * [2] Invoking `stringSmash` with `['a', 'b', 'c' ]` will return `abc`.
 */
-function stringSmash(/* code here */) {
-  /* code here */
+function stringSmash(strings) {
+  return strings.reduce((first, last) => first += last);
 }
 
 // A local community center is holding a fund raising 5k fun run and has invited
@@ -358,7 +361,7 @@ if (typeof exports !== 'undefined') {
   if (processSum) { module.exports.processSum = processSum }
   if (processProduct) { module.exports.processProduct = processProduct }
   if (processDuplicateFree) { module.exports.processDuplicateFree = processDuplicateFree }
-  if (lowerCaseStrings ) { module.exports.lowerCaseStrings = lowerCaseStrings}
+  if (lowerCaseStrings) { module.exports.lowerCaseStrings = lowerCaseStrings }
   if (isItAnApple) { module.exports.isItAnApple = isItAnApple }
   if (removeApple) { module.exports.removeApple = removeApple }
   if (stringSmash) { module.exports.stringSmash = stringSmash }