How far did you get?

I'm sure you got stuck here. The thing we need to do now is multiply by the conjugate of the numerator:

This simplifies to

Expand out the numerator, and try to cancel out as many terms as you can. Then a common factor of h should appear in all the numerator terms. Pull it out, and it should then cancel out with the h term in the denominator. Then evaluate the limit.

Can you try to take it from here?

--Chris