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).