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\left \{ {{4x-y=9} \atop {3x+7y=-1}} \right\left \{ {y=4x-9} \atop {3x+7(4x-9)=-1}} \right. . \\

3x+28x-63=-1\\

31x=62\\

x=2\\

y=4*2-9\\

y=-1\\

Ответ:(2;-1)