Question: how to find the surface area of a water tank?
Answer: For a rectangular tank with the length l = 4 cm, width w = 5 cm and height h = 7 cm, we can calculate its surface area like so: A = 2lw + 2lh + 2wh. A = 2 * 4 * 5 + 2 * 4 * 7 + 2 * 5 * 7 = 166 cm.