The diagonals of quadrilateral QRST intersect at Upper P left parenthesis negative 1 comma 3 right parenthesis. QRST has vertices at Upper Q left parenthesis 1 comma 6 right parenthesis and Upper R left parenthesis negative 4 comma 4 right parenthesis. What must be the coordinates of Upper S and Upper T to ensure that QRST is a parallelogram?