Question 322506
The roof radius is given in feet. Convert that to inches

20*12=240 inch radius. The area of the roof in square inches is then

pi*(240)^2=57600pi=180955.74 in^2/hour.

Since the rain falls at an inch an hour, we also have 57600Pi cubic inches of rain in one hour.

A gallon is 231 of these. So, in one hour {{{57600Pi/231=783.36}}} gallons per hour.

Now, you should be able to finish the last few parts of the problem.