Answer
$$S(2,-3)$$
Work Step by Step
Parallelogram is type of rectangle, whose opposite sides are parallel.
We also know, that diagonals are also bisects and they cross in the middle of the diagonals. So midpoints of diagonals are the same and we can use it to calculate $S(x,y)$.
$M_{PR}=(\frac{4-1}{2}, \frac{2-4}{2})=(1.5, -1)$
$M_{QS}=(\frac{1+x}{2}, \frac{1+y}{2})=(1.5, -1)$
$\frac{1+x}{2}=1.5$
$1+x=3$
$x=2$
$\frac{1+y}{2}=-1$
$1+y=-2$
$y=-3$
We found $S(2,-3)$
