Expand the numerator.
Combine like terms to simplify the numerator.
Factor out an h.
Simplify the fraction by 'cancelling out' the h.
Evaluate the limit as h→0.
If your answers do not agree, you probably made an Algebraic error in part (a).
also sketch the f '(x) you found in part (a) and part (b).
The two graphs should be close, but not identical since part (c) uses a finite value for h.