CAT 2025 Coordinate Geometry — Previous Year Question

The $(x, y)$ coordinates of vertices $\mathrm{P}, \mathrm{Q}$ and R of a parallelogram PQRS are $(-3,-2),(1,-5)$ and $(9,1)$, respectively. If the diagonal SQ intersects the $x$-axis at $(a, 0)$, then the value of $a$ is