Another way to solve this is to use the Midpoint Formula. The midpoint of a segment joining points 
and 
is
So the midpoint of your segment is
Perhaps it helps to see that the x-coordinate of the midpoint is just the average of the x-coordinates of the points. Ditto for the y-coordinate of the midpoint; just average the y's.
So the midpoint of your segment is
Perhaps it helps to see that the x-coordinate of the midpoint is just the average of the x-coordinates of the points. Ditto for the y-coordinate of the midpoint; just average the y's.