Cheese needs to buy some cardboard to build a box 10 inches long 9 inches wide and 7 inches high. If she purchases 500 square inches of cardboard, how much will be left over?
that's the only possible answer if you think about it.
You know that it's going to be at least more than 100 square inches she uses and none of the other answers are less than 400.
The total surface area of the cardboard needed to build the box is:
2(10x9) + 2(10x7) + 2(9x7) = 180 + 140 + 126 = 446 square inches.
If Cheese purchases 500 square inches of cardboard, she will have 500 - 446 = 54 square inches of cardboard left over.