Here's my problem: A machine is rolling a metal cylinder under pressure. The radius, r, of the cylinder is decreasing at a constant rate of .05 inches per second and the volume, V, remains constant at 128(pi) cubic inches. At what rate is the length, h, changing when the radius is 2.5 inches? So dr/dt= .05 v=128(pi) r=2.5 and I should be able to solve for h using the equation: v=(pi)(r^2)(h) right? So where do I go after this?