To find the volume of this box, we need to do length times width times height. The length here is going to be the 21 minus those two corner pieces, so minus the two XS one on each end. The width is going to be 13 minus those two end pieces or the two XS, those two corners, and the height would just be X when I fold it up. So now we're going to foil. If we foil this out, we're going to get 273 -, 42 X -20 six X + 4 X squared. And then if we distribute the X at the end, we're going to get four X ^3 -68 X squared by combining our like terms and multiplying the X through plus 273 X.