Simplifying the summation

Simplifying the summation

I was studying the iteration method and one sample had this summation:
$\sum_{j=0}^{n-2} (n - j)$
Where this eventually gets simplified as:
$n(n-1) - {(n-2)(n-1)\over 2} $
I did not quite understand how this is achieved. The first step is
obviously split them so:
$ \sum_{j=0}^{n-2} n - \sum_{j=0}^{n-2} j$
but what about the rest?