please help me here.

here is the problem:

Use the formula V = (1/3)pi r2(h) for the volume of a right circular cylinder to find

a. the average rate at which the volume of a right circular cylinder changes with the radius r as r increases from 3 cm to 6 cm.

b. the instantaneous rate at which the volume of the right circular cylinder changes with r when r = 6 cm.

I tried to solve it at home and I arrived at the answers:

a. 3(pi)(h)

b. 4(pi)(h)

Are my answers correct?

thanks