3m + 5
There really is no need to fully solve this equation, here's why.
As you can see all of the answer choices have a constant at the end, -8, 5, -6, and 8. In order to simplify the given expression, you must combine like terms. Within the expression, you have one constant and that's positive 5, leaving 3m + 5 to be the only possible and correct answer choice.
Hope this helps!