Simplify $\frac{1}{h}\Big( \frac{1}{(x-a-h)^2} - \frac{1}{(x-a)^2}\Big)$ 
Simplify $\frac{1}{h}\Big( \frac{1}{(x-a-h)^2} - \frac{1}{(x-a)^2}\Big)$

I would like a little help, so that I can finish solving this exercise.
So far, I've got
$$
\frac{\frac{1}{(x-a-h)^2} - \frac{1}{(x-a)^2}}{h}
= \frac{\frac{(x-a)^2 - (x-a-h)^2}{(x-a-h)^2(x-a)^2}}{h}
= \frac{\frac{(x-a)^2 - (x-a-h)^2}{(x-a-h)^2(x-a)^2}}{ \frac{h}{1}}
= \frac{(x-a)^2 - (x-a-h)^2}{h(x-a-h)^2(x-a)^2}
$$
In the numerator maybe I can continue with a difference of squares, but I'm a little confused.

hint
Begin by putting
$$x-a=b$$
then
$$\frac{1}{(b-h)^2}-\frac{1}{b^2}=$$
$$\frac{b^2-(b-h)^2}{b^2(b-h)^2}=$$
$$\frac{h(2b-h)}{b^2(b-h)^2}.$$
And if we divide by h, one find
$$\frac{2(x-a)-h}{(x-a)^2(x-a-h)^2}.$$
