Why isn’t my code working? Math.max isn’t returning anything.

```
function largestOfFour(arr) {
var newArray = {}
// You can do this!
for (x = 0 ; x < arr.length;x++){
Math.max.apply(Math, arr[x])
}
}
largestOfFour([[4, 5, 1, 3], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);
```

TIA,

Gabriel