x-30%x=4分之3
70%x=3/4
7/10x=3/4
x=3/4÷7/10
x=3/4×10/7
x=15/14
3-70%x=0.2
70%x=3-0.2
0.7x=2.8
x=2.8÷0.7
x=4
50%x+25=80
0.5x=80-25
0.5x=55
x=55÷0.5
x=110
希望对你有所帮助