Hey there!
On this problem, we have to combine like terms. A like term in this sense doesn't have to have the same coefficient, but it has to have the same variable.
Our like terms are 2m and 4m, along with 3 and 5.
When we add 2m and 4m we get 6m, and when we add 5 and 3 we get eight.
Notice how 5 and three are like terms because they're both whole numbers and don't have any variables.
Your solution is 6m + 8.
My advice to you is pay attention to your like terms and don't mix them up. A strategy is to underline like terms in the same color.
Hope this helps!