从事K12教育行业多年
4(y-2)-{5(1-2y)-4(5y-1)}=0
4y-8-(5-10y-20y+4)=0
4y-8-(9-30y)=0
4y-8-9+30y=0
4y+30y=8+9
34y=17
y=17/34
y=1/2