Per hour?

[/quote]A. What is the total amount of water supplied per hour inside a circle of radius 18?

B. What is the total amount of water that goes through the sprinkler per hour[/QUOTE]

Imagine a small "piece" of that circle of area dA. The volume of that piece to a depth of is [tex]e^{-r}dA[/itex] you want to integrate that.

In polar coordinates, dA is so for part (A) you need . For part (B) this is no restriction on r so it is