Ответ:

1) 7х+3=30-2х

7х+2х=30-3

9х=27

х=27÷9

х=3

2) 0,2х+2,7=1,4-1,1х

0,2х+1,1х=1,4-2,7

1,3х=-1,3

х=-1,3÷1,3

х=-1

3) 3/8х+15=1/6х+10

3/8х-1/6х=10-15

9/24х-4/24х=-5

5/24х=-5

х= -5/1÷5/24=-5/1×24/5=-24/1=-24

х=-24