Respuesta :

1219639655

Answer:

x=7

Step-by-step explanation:

3x+9x=6x+42 add simalar  elements 3x+9x=12x

12x=6x+42

12x-6x=6x+42-6x subract 6x from both sides

6x=42 simplify

6x/6=42/6 divide both by 6

x=7