formula for volume = V=PI x r^2 x H so replace letters with known values and work the problem out
215 in.^3 = 3.14 x r^2 x 7.5
215/(7.5x3.14) = r^2/(7.5 x 3.14)
r^2 = (215/7.5x3.14)
r^2 = 9.1295
Now, taking the square root of both sides, we get:
sqrt(r^2) = r
sqrt(9.1295) = 3.021
r = 3 inches