algebra precalculus - Simplifying $left(frac{a-b}{sqrt a+sqrt b}+sqrt bright)/left(frac{a-b}{sqrt a+sqrt b}-sqrt aright)$

It was really a long time since I did math at school and now I'm preparing for a admission test to college.
I took a look at the older tests and immediately got stuck at the first question. It really feels like I have to shape up.
Anyway so here's the equation:

$$x = \frac{\frac{a-b}{\sqrt a+\sqrt b}+\sqrt b}{\frac{a-b}{\sqrt a+\sqrt b}-\sqrt a}$$

...and it is supposed to end up in $-\sqrt\frac{a}{b}$

I tried a few different ways of doing it, but always end up wrong. I don't wanna post my attempts here since I honestly don't seem to know what I'm doing. Also this is my first post here on math.stackexchange.com so please tell me if I'm doing something wrong. Any help is greatly appreciated (with the problem).