59/100 would be your answer. Hope this helps!
In this equation you have 3m+3=15 or 3m+3=-15. Solving for m on both you get m=4 or m=-6. The answer is D.
-4x+56=24
-56=-56
———————
-4x =-32
-32/-4x
X=8
A is a function because you have a different value for x.
B is not a function because you can't have the x value have a number twice, in this case it's 2.
C is not a function for the same reason as B.
D is a function because there is always a different x value.
Hope I didn't mess up for your sake