a)5x-2x=12-3

3x=9

x=3

b)7x-9x=-8+6

-2x=-2

x=1

c)x+3x=-11+9

4x=2

x=1/2

d)7x-5x=7+2

2x=9

x=9/2

e)12x+x=-27+5

13x=22

x=22/13

a.

5x+3=2x+12

5x+3-2x=2x+12-2x

3x+3=12

3x+3-3=12-3

3x=9

x=9/3

x=3

b .

7x - 6 = 9x - 8

7x - 6-9x = 9x - 8-9x

-2x-6=-8

-2x-6+6=-8+6

-2x=-2

x=-2/-2

x=1

c.

x +9 = -3x - 11

x+9+3x=-3x+11+3x

4x+9=11

4x+9-9=11-9

4x=2

x=2/4

x=0.5

d.

 7x -7  = 5x + 2

7x-7-5x=5x+2-5x

2x-7=2

2x-7+7=2+7

2x=9

x=9/2

x=4.5

e.

12x -5 = x -  27

12x-5-x=x-27-x

11x-5=-27

11x-5+5=-27+5

11x=-22

x=-22/11

x=-2

voilà... :)