x-[3/10x+(3/10x+3)=20%x请帮忙解一下,急~~~~要写出过程哦!

x-20%x=3/10x+(3/10x+3)
80%x=6/10x+3
8/10x=6/10x+3
2/10x=3
x=15

x-[3/10x+(3/10x+3)=20%x
x-0.3x-0.3x-3=0.5x
0.4x-3=0.5x
-0.1x=3
x=3/(-0.1)
x=-30

x-[3/10x+(3/10x+3)=20%x
x-[3/5x+3]=1/5x
2/5x-3=1/5x
1/5x=3
x=15