evvoronina1 3х - 2(3х-1) = 2х + 7
3х - 6х + 2 = 2х + 7
2х + 6х - 3х = 2 - 7
5х = -5
х = -5 : 5
х = -1

Проверка.
1) 3х = 3 • (-1) = -3
2) 2(3х-1) =2• [3(-1) -1] = 2 • (-4) = -8
3) 2х +7 = 2(-1) +7 = -2 + 7 = 5
4) -3 - (-8) = - 3+ 8 = 5
5=5