In my class we recently went over rates of change and while I understood a few of the problems in the homework I just took an exam and really bombed on this one. Where do you even start with this one?

I put down that f'(x) = 3*pi*R^2 (marked wrong for the 3) and that dr/dt = 3*pi*R^2 / 72*pi

but then I didn't know what to do next (assuming that was the right place to start)