Answer
a) 28
b) 75
Work Step by Step
a) The average rate of change is equal to $\frac{V(4)-V(2)}{4-2} = \frac{4^3-2^3}{4-2} = \frac{64-8}{2} = \frac{56}{2} = 28$
b) To find the instantaneous rate, we take the derivative of $V$:
$V'(l) = 3l^2$
$V'(5) = 3(5)^2=75$
