а)

12-2х=3х

3x+2x = 12

5x = 12

x = 12 : 5

x = 2,4

б)

5х-8=9+3х

5x - 3x = 9 + 8

2x = 17

x = 17 : 2

x = 8,5

в)

9х+(6-2х)=15

9x + 6 - 2x = 15

9x - 2x = 15 - 6

7x = 9

x = 9 : 7

x = 1 2/7

г)

2х-(5х+4)=-8

2x - 5x - 4 = -8

-3x - 4 = -8

3x = 8 - 4

3x = 4

x = 4 : 3

x = 1 1/3