The average rate of change of a function [tex]f(x)[/tex] over an interval [tex][a,b][/tex] is
[tex]\dfrac{f(b)-f(a)}{b-a}[/tex]
In this case, it's
[tex]\dfrac{f(4)-f(0)}{4-0}=\dfrac{256-16}4=60[/tex]
