add solution to redux remove item from array (#35593)

guide/english/certifications/front-end-libraries/redux/remove-an-item-from-an-array/index.md

@@ -3,8 +3,32 @@ title: Remove an Item from an Array
 ---
 ## Remove an Item from an Array
 
-This is a stub. <a href='https://github.com/freecodecamp/guides/tree/master/src/pages/certifications/front-end-libraries/redux/remove-an-item-from-an-array/index.md' target='_blank' rel='nofollow'>Help our community expand it</a>.
+### Solution
+```javascript
+const immutableReducer = (state = [0,1,2,3,4,5], action) => {
+  switch(action.type) {
+    case 'REMOVE_ITEM':
+      // don't mutate state here or the tests will fail
+      return [...state.slice(0, action.index), ...state.slice(action.index + 1, state.length)];
+      // or return state.slice(0, action.index).concat(state.slice(action.index + 1, state.length));
+    default:
+      return state;
+  }
+};
 
-<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>.
+const removeItem = (index) => {
+  return {
+    type: 'REMOVE_ITEM',
+    index
+  }
+}
 
-<!-- The article goes here, in GitHub-flavored Markdown. Feel free to add YouTube videos, images, and CodePen/JSBin embeds  -->
+const store = Redux.createStore(immutableReducer);
+```
+
+### Notes
+* array.slice(fromIndex, untilIndex) returns a new array
+* 1st slice from the first item's index (0 inclusive) until indexToRemove(action.index exclusive)
+* 2nd slice from item right after indexToRemove (action.index + 1 inclusive) until length (last item's index + 1 exclusive)
+* since slice returns a new array, combine both parts with [...array1, ...array2] spread operator
+* or combine them with .concat()