Question 1116563
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x-4y=3
x+7y=-8
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{{{system(x-4y=3,-x-7y=8)}}}

{{{(x-4y)+(-x-7y)=11}}}

{{{-11y=11}}}

{{{highlight(y=-1)}}}

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{{{system(7x-28y=21,4x+28y=-32)}}}, and you may know what to do next...