A square has four equal sides therefore you know the perimeter is 20+20+20+20 = 80. Since the square and the rectangle have the same perimeter the perimeter of the rectangle is also 80. We already know that two of the sides are 28 cm long so we can subtract those two sides from 80. That gives us 24 which is the sum of the two remaining sides. Each of these sides is 24/2 which is equivalent to 12. The formula for area of a rectangle is length times width. Your length is equal to 28 and your width is equal to 12. When you multiply these you get 336 which is your final answer.
