I feel like this one might be a pretty easy question

-29

Step-by-step explanation:

replace the variables with the numbers provided. m = -4 so replace the m in the equation with -4:

3 - (-4)n

same thing with the n.  n=-8 so replace the n in the equation with -8:

3 - (-4)(-8)

and then all you have to do after that is solve it using PEMDAS

multiply -4 and -8 first:

3 - 32

then solve 3-32 and you end up with -29.