4x-7y=6/(x-7y)=-9?
Split into two equations:
4x-7y=-9⇒12x-21y=-27
6=-9(x-7y)=-9x+63y⇒-3x+21y=2
So 9x=-25, x=-25/9.
Since 4x-7y=-9, -100/9-7y=-9, 7y=9-100/9=(81-100)/9=-19/9, y=-19/63.
SOLUTION: (-25/9,-19/63)
CHECK
-100/9+19/9=6/(-25/9+19/9)=-9,
-81/9=6/(-6/9)=-9,
-9=-9=-9 OK!