#### Answer

(a) 2
(b) $\frac{2}{3}$

#### Work Step by Step

(a) We calculate the net change between the two points given:
Net change = $f(4)-f(1)=5-3=2$
(b) We calculate the average rate of change between $(1,3)$ and $(4,5)$:
Average rate of change = $\frac{5-3}{4-1}=\frac{2}{3}$