1.2x=81.6
x=81.6/1.2
x=68
（27.5-3.5）/x=4
24/x=4
x=24/4
x=6
x-0.7x=3.6
0.3x=3.6
x=3.6/0.3
x=12
91/x=1.3
x=91/1.3
x=70