3x+2y=40
2y=40-3x
y=20-(3/2)x
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6x-(20-(3/2)x)=20
6x-20+(3/2)x=20
6x+(3/2)x=40
(15/2)x=40
x=16/3
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6(16/3)-y=20
32-y=20
-y=-12
y=12
-------------------------------------
6(16/3)-(12)=20