For first cylinder Vloume = pi * r^2 * h where h is the height and r is the radius so by substitute 6908=pi * r^2 * 22 so r = 9.99 cm For second cylinder Vloume = pi * r^2 * h by substitute 7884.54 = pi * r^2 * 31 so r = 8.99 but the diameter is the required so d= 2*r = 2*8.99 d= 17.99 cm