Next work out the areas of the rectangular faces. The area of a rectangle is length multiplied by width. 7 × 3 = 21, 7 × 4 = 28, 7 × 5 = 35. These areas are added together. 21 + 28 + 35 = 84.

Learn about the surface area and volume of prisms with this BBC Bitesize Maths article. For students between the ages of 11 and 14.