2x - y = 4, (1) x + y = 5. (2) Add the two equations. The "y"-s will cancel and you will get a single equation for only one unknown x: 2x + x = 4 + 5 = 9 ====> 3x = 9 ===> x == 3. Thus you just found one unknown, x. It is 3. Next, to find y, substitute x= 3 into equation (2) and get y = 5 - x = 5 - 3 = 2. Answer. The solution is xx = 3, y = 2.