Since each side has the same length sides, all we have to do is calculate the area of one side and multiply it by 6 as a cube has 6 sides.
To find the surface area, all you do is multiple the length * width. In this case, we are give 20, so you just multiple 20 by 20 to get 400.
All we do now is mutiply 400 by 6 to get 2400
