The average rate of change is given by
[tex]A(x)=\frac{f(b)-f(a)}{b-a}[/tex]
where
a = -2
b = 8
f(a) = f(-2) = -12
f(b) = f(8) = -16
then
[tex]A(x)=\frac{(-16)-(-12)}{8-(-2)}[/tex]
[tex]A(x)=\frac{-4}{10}=-\frac{2}{5}[/tex]
then the average rate of change between [-2 , 8] is -2/5 or -0.4
