Answer
About $-{{\$}} 0.088$ per year, which is less than than the slope of the regression line.
Work Step by Step
The average rate of change of $f$ over the interval $[a, b]$ is given by:
Average rate of change of $f\displaystyle \ \ =\frac{f(b)-f(a)}{b-a}$
The units of the average rate of change of $f$ are units of $f(x)$ per unit of $x$.
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Over $[2,10]$, the average rate of change for $f$
was
$\displaystyle \approx\frac{1.0-1.70}{10-2}=\frac{-0.7}{8}\approx-0.0875\approx-0.088$ (dollars per year)
the slope of the regression line is about
$\displaystyle \frac{0.98-1.46}{10-2}=-\frac{0.52}{8}=0.065$ (dollars per year)
So, the average rate of change is LESS than the slope of the regression line.
