5y+7(3-y)=3(5-2y)-6
5y+21-7y=15-6y-6
5y-7y+6y=15-6-21
4y= -12
y=-12:4
у= - 3
7у-4(3у+5)=2-3(4у-9)
7у-12у-20=2-12у+27
7у-12у+12у=20+2+27
7у= 49
у=49:7
у=7
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(это проверка)
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5y+7(3-y)=3(5-2y)-6
5y+21-7y=15-6y-6
5y-7y+6y=15-6-21
4y= -12
y=-12:4
у= - 3
7у-4(3у+5)=2-3(4у-9)
7у-12у-20=2-12у+27
7у-12у+12у=20+2+27
7у= 49
у=49:7
у=7
________________________________________________________________
(это проверка)
=============================================================
___________________________________________________________