The radius r, height h, and volume V of a right circular cylinder

The radius r, height h, and volume V of a right circular cylinder are related by the equation V = πr²h.

a) How is dV/dt related to dh/dt if r is constant?
b) How is dV/dt related to dr/dt if h is constant?
c) How is dV/dt related to dr/dt and dh/dt if neither r nor h is constant?