In doing these related rates words problem, there is one small step I don't understand....wondered if someone could tell me how it is being done.

How do you go from

dV/dt = [(pi/4) * (h^2)] * dh/dt

to

dh/dt = [4 / (pi * h^2)] * dV/dt

So basically, I'm not sure how they are going from (pi/4) h^2 to 4/(pi h^2)

In another problem I am doing, I want to get dV/dt by itself from this equation:

dS/dt = 12s dV/dt

and I'm not sure how the 12s part would be changed as a result of pulling the dV/dt to the other side