Hello fellow Mathematicians!

I am working on some pratice problem and I have the answer sheet for it but no work. I keep getting the wrong answers so it would be great if someone can help me or at least guide me toward the steps for getting the answers. I really want to learn how to solve it. I have read the book chapter on related rates but O need to kind of wrap my head around these problems any conceptual explanation is great too! Thanks!

1.

Gravel is being dumped from a conveyor belt at a rate of 50 cubic feet per minute. It forms a pile in the shape of a right circular cone whose base diameter and height are always the same. How fast is the height of the pile increasing when the pile is 21 feet high?

Recall that the volume of a right circular cone with height h and radius of the base r is given by

The answer is 0.144

2. A spherical snowball is melting in such a way that its diameter is decreasing at rate of 0.2 cm/min. At what rate is the volume of the snowball decreasing when the diameter is 10 cm. (Note the answer is a positive number).

Answer: 31.41

So I know the formula for a sphere is

so do I plug in the r, which is .1. and then do the derivative of it? Isn't .2 cm/min the derivation already? thanks3.