Answer
About $-{{\$}} 0.02$ 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
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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$d.$
Over $[2,10]$, the average rate of change for $f$ was
$\displaystyle \approx\frac{6.50-6.34}{10-2}=\frac{-0.16}{8}=-0.02$ dollars per year
The slope of the regression line is:
$\displaystyle \frac{6.32-6.44}{10-2}=\frac{-0.12}{8}=-0.015$
So, the average rate of change is LESS than the slope of the regression line.
