Question 113699
X+Y=-9 OR X=-9-Y 
NOW SUBSTITUTE (-9-Y) FOR X IN THE OTEHRE EQUATION 7 SOLVE FOR Y
3(-9-Y)-Y=-7
-27-3Y-Y=-7
-4Y=-7+27
-4Y=20
Y=20/-4
Y=-5 ANSWER.
X-5=-9
X=-9+5
X=-4 ANSWER.
PROOF
3*-4-(-5)=-7
-12+5=-7
-7=-7