Me with a and b. and gave me the answer and how you got to the answer.

the answer is 12m + 4

Step-by-step explanation:

you do the distributive property which is 3*2m and then 3*4 and you get 6m+12 and then you do it again which you do 2*3m and then 2*-4 and you get 6m-8 and then you get 6m+12+6m-8 and you just add your like terms to get 12+4

                                                hope this helped