**Aim of the puzzle**: Declare a variable to use locally inside a function

**Walk through of solution**:

In some functions, it is necessary to declare a variable to store a value, and then return that variable at the end of the function.

In this puzzle, the `sum()`

function will take an array of numbers, and return the sum of those numbers.

Inside the function, declare a variable to store the sum. Set its value to `0`

to start.

Then, add a for loop to iterate through the array, and inside the code block, use the `+=`

operator to add each number in the array to the local variable.

At the end of the function, below the for loop, return the local variable.

**Sample code solution**:

```
let numbers = [2,3,5];
function sum(numberArray) {
let sum = 0;
for (let num of numberArray) {
sum += num;
}
return sum;
}
console.log(sum(numbers));
```

**Javascript Concepts**: Variables, Functions, Output, For Loops, `+=`

Operator, Return Statements