Answer
$\$ 1.33 $ per month
Work Step by Step
The average rate of change of $f(x)$ over the interval $[a, b]$ is $\displaystyle \frac{f(b)-f(a)}{b-a}$
Units: "(unit of f(x) ) per (unit of x)"
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Given the interval $[2,5]$ and the graph,
a=$2,\ \quad (2,23)$ on the graph $\Rightarrow f(2)=23$
b=$5,\ \quad (5.27)$ on the graph $\Rightarrow f(5)=27$
$\displaystyle \frac{f(b)-f(a)}{b-a} =\displaystyle \frac{27-23}{5-2}=\frac{4}{3}$ (dollars per month)
$\approx\$ 1.33 $per month
