Ответ:

(3х+8)-(9х+14)=9

3х+8-9х-14=9

3х-9х=9-8+14

-6х=15

х=15/-6=-5/2

10х+3(7-2х)=13+2х

10х+21-6х=13+2х

10х-6х-2х=13-21

2х=-8

х=-4

-6(х+2)=4х-17

-6х-12=4х-17

-6х-4х=12-17

-10х=-5

х=-5/-10=1/2