①
②x:21=:
③160×25%-1.3x=17.9
0.6∶1.8=89x 1.252.5=3.8x
5x-15x=19.2 30%x+25=40
1+12x=1.6 25%x-9%x=48 3.2:x=25:12
25x=4.2 x÷19=27 74:x=6:0.3