First, use the formula volume = pi * r^2 * height- you have the volume, so just solve the equation 411pi = pi * 9 * r^2 for r, and you get that r = 6.75. Since diameter is equal to 2r, multiply 6.75 by 2 to get your answer of 13.5 inches. The questions asks for the diameter in centimeters though, which makes it 34.3 cm.
Hopefully this helps- let me know if you have any questions!
