The vector that goes from A to the midpoint AB shall be called v.
Now, do you see that if we take v and place it at AB, we will end up at B?
So that will give us a way to do all the calculations
v = AB - A = (-2,4) - (3,-2) =(-2-3, 4-(-2)) = (-5,6)
So then
B = AB + v = (-2,4) + (-5,6) = (-7,10)