0.9÷（x +0.4）=0.45；x+0.4=0.9/0.45=2;x=2-0.4=1.6
x=0.9÷0.45-0.4=2-0.4=1.6
0.9÷（x +0.4）=0.45(x+0.4)*0.45=0.9x+0.4=2x=2-0.4x=1.6
1.6
