I'm stick on differentiating, from first principles, the following function:

f(x) = (3x-1)/(x+2)

I plug that into:

[f(a+h) - f(a)]/h

and I get:

7h/(x+h+2)(x+2)

But when I use the quotient rule to do it, I end up with:

7/(x+2)^2

I've been trying to get rid of that bothersome h, but I just haven't found a way to do it! I have a feeling that I'm overlooking something really simple. Any help appreciated.