3(2y-3)-y的值与-7(1-y)互为相反数
3(2y-3)-y+[-7(1-y)]=0
6y-9-y-7(1-y)=0
6y-9-y-7+7y=0
6y+7y-y-9-7=0
12y-16=0
3y-4=0
3y=4
y=4/3