Question

2x - 3y = -4 if x + 3y = 7

Answer 1

(2x-3y=-4)-2(x+3y=7)

2x-3y-2x-6y=-4-14

-9y=-18

y=2, making x+3y=7 become:

x+6=7

x=1

So the solution to the system of equations is the point (1,2)

Answer 2

Leave x alone on one side.

x = 7 - 3y

Substitute into equation

2(7 - 3y) - 3y = -4

Distribute

14 - 6y - 3y = -4

Solve

14 - 9y = -4

14 + 4 = 9y

18 = 9y

y = 18/9

y = 2
x = 1