Respuesta :

Answer:

m = 8.

Step-by-step explanation:

Arithmetic mean 18 = (12 + 3m)/2

Cross multiply:

12 + 3m = 36

3m = 36 - 12 = 24

m = 24/3 = 8.

Check this answer:

(3(8) + 12)/2

= (24 + 12)/2

= 36/2

= 18.