The place where your "m" is already correct.
Additive inverse of -3(1/4) would be a number which when added to -3(1/4) would equal to 0. (zero)
This number is 3(1/4).
-3(1/4) + 3(1/4) = 0
If you were to count, it takes 8 little of those lines/stems thingy in order to reach the whole next number.
(1/4) of 8 is 2 so "m" would be at 2 little line/stems to the right of 3 which is where you already left it at.