Question

Solve the system of equations. -x - 3y = 20 -x + 4y = -36

Answer 1

Multiply the second equation by 1 to make it positive then add them together.
-x-3y=20
+x-4y=36
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-7y=56
y=-8

Plug that into one of the equations above.
-x-3(-8)=20
-x+24=20
-x=20-24
-x=-4
x=4

So x=4 y=-8 or (4,-8)

Hope that helps