Volume = (PI * r^2 * h) / 3
r^2 = (3 * Volume) / (PI * h)
r = Square Root (3 * Volume) / (PI * h)
Step-by-step explanation:

check the picture below.
make sure your calculator is in Degree mode.
78.5/100 as a decimal is just 0.78.5 and as a percent it is 78.5 %