X - y = 3 (line a)

x + y = 3 (line b)

(0, - 3)

(0, 3)

(-3, 0)

(3, 0)

Answer. You must first put the equation into slope-intercept form (y = mx + b). To do this, subtract x from both sides to isolate y. Then, since y will be negative, divide each side by - 1, resulting in y = x - 3.