If the side length of the original tile is x, then the area is length * width, or x*x which is x^2. That's the first box up there. The new length is x - 4, since the length is what he cut away from. That's the second box up there. The width is still x, so the third box is x, and the area removed is 4x, the last box. So here's your info: box 1: x^2; box 2: x - 4; box 3: x; box 4: 4x
