Method 1: 6 cm is the height, ∫2πr = 4, ∴r=2/π, ∴ volume =πr? *6=24/π≈8cm？

Method 2: 4 cm is the height, ∫2πr = 6, ∴r=3/π, ∴ volume =πr? *4=36/π≈ 12cm？

So the maximum volume is 12cm?