add solution ironhack-labs#4.1

Author: droidsam1

src/functions-and-arrays.js

@@ -60,7 +60,13 @@ function sum(input) {
 // Level 1: Array of numbers
 const numbersAvg = [2, 6, 9, 10, 7, 4, 1, 9];
 
-function averageNumbers() {}
+function averageNumbers(input) {
+  if (!input || input.length === 0) {
+    return null;
+  }
+  let sumElements = sum(input);
+  return sumElements/input.length;
+}
 
 // Level 2: Array of strings
 const wordsArr = ['seat', 'correspond', 'linen', 'motif', 'hole', 'smell', 'smart', 'chaos', 'fuel', 'palace'];