7分之1:8分之1=8:x
7/1x=8/1*8=1
x=1÷7/1
x=7
4分之1x=5分之1:2
2x=4×5/1=5/4
x=5/4÷2
x=5/2
2分之1.8=5分之x
8x=2/1×5=2/5
x=2/5÷8
x=16/5
3分之20:x=40:1
40x=3/20×1
x=3/20÷40
x=6/1
3(x+2)=39.3
x+2=39.3÷3=13.1
x=13.1-2
x=11.1
2*(5.5-x)=4.4
5.5-x=4.4÷2=2.2
x=5.5-2.2
x=3.3
5*(x+2)=32
x+2=32÷5
x+2=6.4
x=6.4-2
x=4.4