0.4X/(X+5)=0.3
0.4X=0.3（X+5)
0.4X=0.3x+1.5
0.4x-0.3x=1.5
0.1x=1.5
x =15(40%*15+y)/(15+5+y)=50%这个呢(40%*15+y)/(15+5+y)=50%(6+Y)/(20+Y)=0.56+Y=0.5×（20+y)6+y=10+0.5yy-0.5y=10-60.5y=4y=8