15х+10=7+12у 15х-12у=7-10 15х-12у=-3 15*(31-4у)/(5) -12у=-3
4х+4у+х=31 5х+4у=31 х=(31-4у)/5 х=(31-4у)/5
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93-12у-12у=-3 93-24у=-3 у=4 у=4
х=(31-4у)/5 х=(31-4у)/5 х=(31-4у)/5 х=(31-4*4)/5
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у=4
х=3