You know 4 is really close to six, so even if you put y as two, 4x2 is 8 and you can't add anything to get to six, so you can automatically tell it is 1. Knowing that, you can easily solve X. Ask yourself "What do you add to 4 to get 6?) and you get 2. In the next problem, 1+2 is 3, which proves your answer.