x除9=20
x=20×9
x=180
2.1x=0.84
x=0.84÷2.1
x=0.4
x除1.5=3
x=3×1.5
x=4.5
5x=40
x=40÷5
x=8
x除0.7=1.2
x=1.2×0.7
x=0.84
18x=360
x=360÷18
x=20