Answer
($A$)
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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$b.$
Over $[2,7]$, the average rate of change for $f$ was
$\displaystyle \approx\frac{6.10-6.34}{7-4}=\frac{-0.24}{3}=-0.08$
and for the regression line:
$\displaystyle \frac{6.38-6.42}{7-4}=\frac{-0.04}{3}=-0.013$
so the answer is: ($A$)
