I know this looks like a dumb question, but how do I simplify this? Does it uses some square root property or factorization? The wolfram alpha has no step-by-step solution for this, so it may use some crazy technique, I guess.
$$\frac{\sqrt{4+h}-2}{h} = \frac{1}{\sqrt{4+h}-2}$$
Hint: Multiply with $$\sqrt{4+h}+2$$ both the numerator and the denominator. The RHS shoud be $$\frac{1}{\sqrt{4+h}+2}$$ and not with $-2$ as you have it.