Put the two points like an equation with point A on top and midpoint M on the bottom like this:
A (-4,8)
M (1,7.5)
Now, look at the difference between the x points of point A and midpoint M. The difference is +5. Do the same for the y points between point A and M. The difference is -0.5. From point M, add 5 to 1 (which is the x point of M) and subtract 0.5 from 7.5 (which is the y point of M). Now you have (6,7) which is point B. I hope this helped!! :)
