5x + 4y = 12 (1)
3x - 3y = 18 divide through by 3 → x - y = 6 .....
multiply through by 4 → 4x - 4y = 24 (2)
Add (1) and (2)
9x = 36 divide through by 9
x = 4
Using x - y = 6, we have
4 - y = 6 add y to both sides, subtract 6 from both sides
4 - 6 = y = -2
