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):

"A trough is 10 ft long and its ends have the shape of isosceles triangles that are 3ft across at the top and have a height of 1 ft. If the trough is being filled with water at a rate of (12 ft^3)/min, how fast is the water level rising when the water is 6 inches deep?"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!