# Related rates help

1. Assume that the radius r of a sphere is expanding at a rate of 50 cm/min. The volume of a sphere is V= 4/3 πr^3 and its surface area is 4πr^2.Determine the rate of change of volume when r = 13 cm

2. I tried d/dr=8*13*50*pi

3. 5200pi but is wrong