you can solve this by substitution. First, find y. x + y =7 -x on both sides
y = x -7 now substitute in second equation. 3x - (x-7) = 1 +7 on both sides 3x - x = 8 2x = 8 x = 4 now that you know x = 4, substitute it into the first equation y + (4) = 7 y = 3