The browser storage localStorage is not available. Either your browser does not support it or you have disabled it or the maximum memory size is exceeded. Without localStorage your solutions will not be stored.

# Functions call functions

Functions can call other functions:

```
function gross(net) {
let vat = 20;
let tax = net * vat / 100;
return net + tax;
}
function addWithVat(netX, netY) {
let grossX = gross(netX);
let grossY = gross(netY);
return grossX + grossY;
}
```

`addWithVat`

takes two net amounts and returns the sum of the gross amounts.
`gross`

calculates the gross amount from a net amount. Thereby a value added tax of 20% is assumed.
Instead of calculating the gross amount itself, `addWithVat`

use the function `brutto`

.
This has two advantages: The code is easier to read and the gross calculation is performed centrally in one place.## Exercise

Write a function

`sum`

that takes an array of numbers and returns the sum of these numbers.
Write a function `mean`

that takes an array of numbers and returns the average of these numbers.
The `mean`

function should use the `sum`

function.