Integration with a square root at the bottom

So I was reviewing my examples, and one of them looked like this:
http://img217.imageshack.us/img217/4295/mathzx1.jpg
and that u = 4x + 1, therefore du = 4dx. But how did the first step above turned into the next step? I can't seem to see how the next part came to be.

Actually, the substitution given is