Volume of a cylinder = πr²h. Substitute r=16 and h=64: volume = 3.14 × 16 × 16 × 64 = 51445.76 cubic mm. Think of a cylinder as many equal circular layers stacked up. So we find the circular base area πr² and multiply by the height. The answer is in cubic units, so the correct choice is 51445.76 mm³.