Answer
$0.3$
Work Step by Step
The average rate of change of $f(x)$ over the interval $[a, b]$ is $\displaystyle \frac{f(b)-f(a)}{b-a}$
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Given the interval $[-3,1]$ and the table,
a=$-3,\ \quad f(-3)=-2.1$
b=$-1,\ \quad f(-1)=-1.5$
$\displaystyle \frac{f(b)-f(a)}{b-a} =\displaystyle \frac{-2.1-(-1.5)}{-3-(-1)}$
$=\dfrac{-2.1+1.5}{-3+1}=\dfrac{-0.6}{-2}=0.3$
(no units)
