Respuesta :

- 9x - 12 = 8 - 4x
- 9x - 12 (+ 12) = 8 (+ 12) - 4x
- 9x = 20 - 4x
- 9x (+ 4x) = 20 - 4x (+ 4x)
- 5x = 20
- 5x (/ - 5) = 20 (/ - 5)
x = - 4

I hope this helps :)