For a better understanding of the solution provided here please find the diagram attached.
Please note that in coordinate geometry, the coordinates of the midpoint of a line segment is always the average of the coordinates of the endpoints of that line segment.
Thus, if, for example, the end coordinates of a line segment are
and
then the coordinates of the midpoint of this line segment will be the average of the coordinates of the two endpoints and thus, it will be:

Thus for our question the endpoints are
and
and hence the midpoint will be:


Thus, Option C is the correct option.