Question

A conical salt spreader is spreading salt at a rate of 1 cubic feet per minute. The diameter of the base of the cone is 4 feet and the height of the cone is 5 feet. How fast is the height of the salt in the spreader decreasing when the height of the salt in the spreader (measured from the vertex of the cone upward) is 3 feet? Give your answer in feet per minute.

Answer 1

I understand the first part, but confused about the second.

Answer 2

you want dh/dt so replace the r in the volume equation in terms of h.