I read my book and understood what the book was saying but when I try to do the problems, I just can't seem to get them right and I am having a lot of trouble with them. Here is 1 of my 3 questions (the 2 other questions were posted each in their own thread):

"Gravel is being dumped from a conveyor belt at a rate of (30 ft^3)/min, and its coarseness is such that it forms a pile in the shape of a cone whose base diameter and height are always equal. How fast is the height of the pile increasing when the pile is 10 ft high?"If someone could explain how to solve this problem in detail, it would be greatly appreciated! I attached my work (even though I think that I am so lost that it's kind of pointless to attach).

Thanks in advance!