Question

Find x + y: -3x + 7y = -16
-9x + 5y = 16

Answer 1

Solve for y in the first eqn

y=(-16 +3x)/7

Substitute into second eqn
-9x+5((-16+3x)/7)=16
Distribute the 5
-9x - 80/7 + 15x/7 = 16
Multiple everything by 7 (to get rid of fraction)
-9(7)x -80 + 15x = 112
Simplify
-63x - 80 +15x = 112
-48x -80 =112
-48x=192
x=-4


Substitute into first eqn
-3(-4)+7y=-16
12 + 7y = -16
7y= -28
y = -4


x+y= -4 + -4 = -8