Okay, so after all your help, I think I have an answer.
How I got my answer:
I started by focusing on the middle, we have -2 (m-3n) + 4n, I'm going to go
-2 x - 3n, as deveno pointed out, 2 negative make a positive so -2 x - 3n = 6n, I'm then going to do -2 x m which will give me -2m so...