Write a differential formulas that estimates the change in t

Write a differential formulas that estimates the change in the volume V=(4/3)PIr^3 of a sphere when the radius changes from a to a+dr. Then use the formula to estimate the change in volume when r changes from 40 cm to 40.05 cm.

Formula is change V=4PIa^2dr
I need to know the change in volume, exact answer using pi as needed

V= 4/3 pi*r^3 dV/dr = 4pi*r^2 change in volume = 4 *3.14*40*40*.05 =1004.8