Added hints and solutions to Redux exercises (#35244)

* Added hints and solutions to Redux exercises

solution to Redux exercise: Copy an Object with Object.assign

* Added the full code for the solution

guide/english/certifications/front-end-libraries/redux/copy-an-object-with-object.assign/index.md

@@ -3,8 +3,39 @@ title: Copy an Object with Object.assign
 ---
 ## Copy an Object with Object.assign
 
-This is a stub. <a href='https://github.com/freecodecamp/guides/tree/master/src/pages/certifications/front-end-libraries/redux/copy-an-object-with-object.assign/index.md' target='_blank' rel='nofollow'>Help our community expand it</a>.
+The goal of this challenge is to enforce state immutability when state is an object. 
 
-<a href='https://github.com/freecodecamp/guides/blob/master/README.md' target='_blank' rel='nofollow'>This quick style guide will help ensure your pull request gets accepted</a>.
+### Hint 1
+Use the method ```Object.assign({}, obj1, obj2)``` in return. Pass ```state``` as obj1. 
 
+### Hint 2
+The obj2 should be the updated ```{key: value}``` pair of your state.
+
+### Solution
+```
+const defaultState = {
+  user: 'CamperBot',
+  status: 'offline',
+  friends: '732,982',
+  community: 'freeCodeCamp'
+};
+
+const immutableReducer = (state = defaultState, action) => {
+  switch(action.type) {
+    case 'ONLINE':
+      // to enforce state immutability, return a new state object using Object.assign() method
+      return Object.assign({}, state, {status: 'online'});
+    default:
+      return state;
+  }
+};
+
+const wakeUp = () => {
+  return {
+    type: 'ONLINE'
+  }
+};
+
+const store = Redux.createStore(immutableReducer);
+```
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