8/5x-3/4x=17
0.85x=17
x=17÷0.85
x=20
（1+5/6）x=22/5
x=22/5÷11/5
x=2
（3/2-1/2）x=45
2/2x=45
x=45
7/10—3/4x=2/3
3/4x=7/10-2/3
3/4x=1/30
x=1/30÷3/4
x=2/45