#### Answer

$-\frac{1}{4}$ ft/day

#### Work Step by Step

We see from the graph that $W(200)=50$ and $W(100)=75$. We use this information to find the average rate of change for this interval:
$\displaystyle \frac{W(200)-W(100)}{200-100}=\frac{50-75}{200-100}=\frac{-25}{100}=-\frac{1}{4}$ ft/day