The volume of a cylinder is pi*r^2*h
The radius is half the diameter, so 40/2=20, and the radius is 20 ft.
Plugging in: pi*20^2*32=pi*400*32=12800pi=40212.38597
So the volume is about 40212.4 ft^3 and the expression we used is pi*20^2*32
Hope this helped!