well, if you look at the graph, when x = -1, y or f(x) = 4.
and when x = 2, y = 0.
[tex]\bf slope = m = \cfrac{rise}{run} \implies
\cfrac{ f(x_2) - f(x_1)}{ x_2 - x_1}\impliedby
\begin{array}{llll}
average~rate\\
of~change
\end{array}\\\\
-------------------------------\\\\
\begin{cases}
x_1=-1\\
x_2=2
\end{cases}\implies \cfrac{f(2)-f(-1)}{2-(-1)}\implies \cfrac{0-4}{2+1}\implies \cfrac{-4}{3}[/tex]
