(1)18:0.7=x:21,
0.7x=18×21,
0.7x=378,
0.7x÷0.7=378÷0.7,
x=540;
(2)
=12 2.4
,3 x
12x=2.4×3,
12x=7.2,
x=0.6;
(3)
:1 2
=1 5
:x,1 4
x=1 2
×1 5
,1 4
x=1 2
,1 20
x÷1 2
=1 2
÷1 20
,1 2
x=
.1 10