1：1/2x-7=9x-2/6
1/2x-9x=2/6+7
-8.5x=44/6
x=44/51
2:1/5x-1/2(3-2x)=1
1/5x-3/2+x=1
6/5x=5/2
x=5/3
3:2x+1/3-5x-1/6=1
-3x=1-1/3+1/6
-3x=5/6
x=-18/5
4:1/7(2x+14)=4-2x
2/7x+2=4-2x
16/7x=2
x=7/8
8:3/10(200+x)-2/10(300-x)=300×9/25
60+3/10x-60+2/10x=108
3/10x+2/10x=108
1/2x=108
x=216