Substitute y = 2x+1 from the first equation to the second one x + 3*(2x+1) = 10 x + 6x + 3 = 10 7x = 10-3 = 7 x = 7/7 = 1. Then from the first equation y = 2*1 + 1 = 3. The difference x - y is 1 - 3 = -2. The difference y - x is 3 - 1 = 2.