You are given the task of making an open-topped box out of a single sheet of cardboard.
The cardboard is a 20 inch by 30 inch rectangle. You build the box by cutting out squares in the four corners of the sheet, then folding up along the pink lines until the sides of the box meet. If the squares cut out of each corner of the sheet are x inches to a side, what are the dimensions of the box? That is, what is length of the box (made out of the 30 inch side), the width of the box (made out of the 20 inch side) and the height of the box (made by folding up the sides)?