So if 7 is the middle x-value, you calculate how far it is from the given endpoint in order to determine how far it is from the other endpoint. So,
7 -5 =2, so the other endpoint must be 2 away from 7 in the opposite direction, 7+2=9
Then repeat with y,
3-1/2=5/2, therefore 1/2 - 5/2 = -4/2= -2
So the point is (9, -2)