Click on a square to the left of the X-ray bar and move it to the X-ray bar to reveal the subtraction problem it contains. Once you determine what the answer to the subtraction problem is, move it over the square on the right side of the X-ray bar that contains the answer. Once you have the problem over its answer, drop the squire to place it. If you choose a wrong square, points will be subtracted from your score and you will still have to find its proper location. Move all problems to their answers to complete the level.