SOLUTION: Please help... Solve the system by substitution: 3x-y=-7 x+y=-9 Thank you so much for your help!

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Question 113699: Please help...
Solve the system by substitution:
3x-y=-7
x+y=-9
Thank you so much for your help!
Answer by checkley71(8403) About Me  (Show Source):
You can put this solution on YOUR website!
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