X-{2/5X-9+〔X-(2/5X-9)〕*2/3+5}=15
x-[2/5x-9+(x-2/5x+9)*2/3+5]=15
x-[(2/5x-9)/3+x*2/3+5]=15
x-[4/5x+2]=15
1/5x=17
x=85
一元一次方程,求X