5у+21-7у=15-6у-6
21-2у=9-6у
21+4у=9
4у=-12
у=-3
5y+7(3-y)=3(5-2y)-6
5y+21-7y=15-6y-6
5y-7y+6y=21+6
4y=27
y=27/4
y=6.75
5у+21-7у=15-6у-6
21-2у=9-6у
21+4у=9
4у=-12
у=-3
5y+7(3-y)=3(5-2y)-6
5y+21-7y=15-6y-6
5y-7y+6y=21+6
4y=27
y=27/4
y=6.75