KöMaL 2025 C1841

In the convex quadrilateral $PQRS$, $QR=4$, $RS=6$, $SP=5$, and the internal angles at vertices $P$ and $Q$ are $60^{\circ}$. Knowing that $2PQ=a+\sqrt{b}$, where $a$ and $b$ are positive integers, find the value of sum $a+b$.