A circle with centre (2,3) and radius 4 intersects the line x+y=3 at the points P and Q. If the tangents at P and Q intersect at the point S(α, β),…

A circle with centre $\displaystyle (2,3)$ and radius $\displaystyle 4$ intersects the line $\displaystyle x+y=3$ at the points $\displaystyle P$ and $\displaystyle Q$. If the tangents at $\displaystyle P$ and $\displaystyle Q$ intersect at the point $\displaystyle S(\alpha, \beta)$, then $\displaystyle 4 \alpha-7 \beta$ is equal to $\displaystyle \_\_\_\_$.