x-(3/10+90)=3/5x-40
x-0.3-90=0.6x-40
x-0.6x=90-40+0.3
0.4x=50.3
x=50.3÷4
x=125.75打错了，是x-(3/10x+90)=3/5x-40x-(3/10x+90)=3/5x-40x-0.3x-90=0.6x-40x-0.3x-0.6x=90-400.1x=50x=500