Answer
(a) $-1$
(b) $-\frac{1}{3}$
Work Step by Step
We are given: $r(t)=3-\frac{1}{3}t$, $t=3, t=6$
(a) We calculate the net change:
$r(6)-r(3)=[3-\displaystyle \frac{1}{3}(6)]-[3-\frac{1}{3}(3)]=1-2=-1$
(b) We calculate the average rate of change:
$\displaystyle \frac{r(6)-r(3)}{6-3}=-\frac{1}{3}$
