Lets draw the parallelogram:
Since diagonals QS and RT divide each other into segments of equal lenght, the diagonal bisect each other.
This means that the intersection point A is the middle point of segment QS (or TR). Therefore, we need to compute the middle point of one of segment.
The middle point formula is
where
By substituting these values into the middle point formula ,we get
which gives
Therefore, the coordinates of the intersection points are (-2, -1).