Curved surface area of a cylinder = 2πrh. So CSA = 2 × 3.14 × 15 × 68 = 6405.6 square m. This excludes the two circular ends. 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 6405.6 m².