Solve by Substitution x+y=5 , 3x+2y=12. x+y=5 x + y = 5 , 3x+2y=12 3 x + 2 y = 12. Since y y does not contain the variable to solve for, move it to the right side of the equation by subtracting y y from both sides. x=−y+5 x = - y + 5. 3x+2y=12 3 x + 2 y = 12.