Answer
a. $\quad 3h$
b. $\quad 3$
Work Step by Step
a.
$f(x+h)=3(x+h)-1=3x+3h-1$
$f(x+h)-f(x)=3x+3h-1-(3x-1)$
$=3x+3h-1-3x+1$
$=3h$
b.
using the result of (a),
$\displaystyle \frac{f(x+h)-f(x)}{h}=\frac{3h}{h}=\quad$ .. reduce h,
$=3$