Problem 6:
Volume is 5 pi cm^3, and height is 15 cm.
5 pi cm^3
Then the area of the (round) base must be --------------
15 cm
or A = (pi/3) cm^2.
We want the radius of the base. The formula for that is pi * r^2.
Equate pi * r^2 and (pi/3) cm^2. "pi" cancels. Then r^2 = 1/3.
The radius of the base is the sqrt of 1/3, which is approx. 0.58 cm.