Solve system of equations for x + y: -4x + 9y = -11 & -3x + 7y =-9

x = -3   and   y = -4

x + y = -3-4 = -7

Step-by-step explanation:

-4x + 9y = -11 (1)

-3x + 7y = -9(2)

multiply through  equation (1) by 3   and multiply through equation(2) by 4

-12x + 27y = -33 (3)

-12x + 28y   = -36 (4)

subtract equation (1) from equation (2)

y = -3

substitute y = -3 into equation (2)

-3x + 7(-3) = -9

-3x -21 = -9

add 21 to both-side of the equation

-3x -21 + 21 = -9 + 21

-3x = 12

divide both-side of the equation by -3

-3x/-3 = 12/-3

x = -4

x = -3   and   y = -4