Answer :

-x - 7y = 9
-x + 9y = -23 
=====
-7y - 9y = 9 - (-23)
-16y = 32
y = -2
===
-x -7*(-2) = 9
-x + 14 = 9
-x = 9 - 14
-x = -6
x = 6

(6 ; -2)
-x-7y=9
-x+9y=-23
---------------------- -

-7y-9y=9+23
-16y=32
y=-2

-x-7(-2)=9
-x+14=9
-x=-5
x=-5/-1
x=5


[-2 , 5]