Answer:
( 9, -35 )
Explanation:
We can figure out how far the midpoint is from point A and just add the same values to the midpoint's coordinates to get the location of point B.
From A to Midpoint in the X direction:
+ 6
From A to Midpoint in the Y direction:
-15
The coordinate of the midpoint is:
( 3, -20)
3 + 6 = 9
-15 + (-20) = -35
The coordinates of B are:
( 9, -35 )