I have been given the masses of 5 cups, each with a different amount of screws inside. I am asked to find the mass of a single screw. The cups themselves are all equal in mass and the screws are all equal in mass as well. I know you are supposed to subtract the cups from each other to eliminate the mass of the cups and just get the screws masses. I am stuck and I can't seem to grasp the concept of how to solve this! Thanks for help.