Respuesta :

Answer:

x=3.

Step-by-step explanation:

3x+12=21.

3x=21-12.

3x=9.

x=3.

Answer:

x = 3

Step-by-step explanation:

3x + 12 = 21

- 12 -12

---------------------

3x = 9

divide by 3 on both sides to isolate

x = 3