7х-3-2х=х+9
7х - 2х - х = 9 + 3
4х = 12
х = 3
============================
13 - 2х + 5 = х - 3
- 2х - х = - 13 - 5 - 3
- 3х = - 21
х = 7
=============================
3х - 10 + 9х = 22х
3х + 9х - 22х = 10
- 10х = 10
х = - 1
=============================
26 - 17 + 2х = 5х
2х - 5х = 17 - 26
- 3х = - 9
х = 3