Answer
$$ - \frac{3}{(a+h+1)(a+1)}$$
Work Step by Step
For part a, replace wherever you see an x with a+h. This gives:
$$ \frac{3}{a+h+1}$$
For part b, replace wherever you see an x with a. This gives:
$$ \frac{3}{a+1}$$
Now, we are asked to plug the answers from a and b into the equation:
$$ \frac {f(a+h)-f(a)}{h}$$
We substitute to find:
$$\frac{\frac{3}{a+h+1} - \frac{3}{a+1}}{h}$$
Lastly, we simplify using the techniques learned in this chapter. This gives:
$$ - \frac{3}{(a+h+1)(a+1)}$$
