A cylindrical vessel of uniform cross-section consisting of a gas of $\gamma=1.5$ is divided into two parts $A$ and $B$ using a piston. Initially the piston is kept fixed such that part $A$ has pressure $p$ and volume $5 \mathrm{~V}$ and the part $B$ has pressure $8 p$ and volume $V$. If the piston is let free and the gas is allowed to undergo adiabatic process, then the final volume of the gas in part $A$ is