This is because the correct formula for this problem is: base x height
Using this formula, you first have to find the base of the trapezoid. Since the square's base is 7 ft, and the triangle's base is 3 ft, you add these together and get 10 ft as a base. For the height, you need the square's height which is 7 ft. Then you multiply and get 70 ft.
If you were to get a different piece of paper and trace the same shape and flip it over to the same position that one of them is in it will be the exact same measurements!
