x + y = 9
x/2y = 1 → x = 2y . 1 → x = 2y
x + y = 9 → 2y + y = 9 → 3y = 9 → y = 9/3 → y = 3
x = 2y → x = 2 . 3 → x = 6
S = {(6, 3)}
