3.5x+x=32.4
4.5x=32.4
x=32.4÷4.5
x=7.2
0.6x（x+0.6)=0.6
0.6x+0.36=0.6
0.6x=0.6-0.36
0.6x=0.24
x=0.24÷0.6
=0.4
25%x-20%=1.8
0.25x-0.2=1.8
0.25x=1.8+0.2
0.25x=2
x=2÷0.25
x=8
20%x÷15%=2
0.2x÷0.15=2
0.2x=2×0.15
0.2x=0.3
x=0.3÷0.2
x=1.5