x = -3
y = -18
step-by-step explanation:
to solve by substitution, substitute one variable and solve for the other. then substitute again to find the remaining variable.
x-1/3(3x-9) = -3 since y=3x-9 substittute y.
x-1/3(3x-9)=-3
x + x +3 = -3
2x+3=-3
2x+3-3= -3-3
2x=-6
x=-3
substitute again into y=3x-9
y=3(-3)-9
y=-9-9
y=-18