2 moles of an ideal gas A is taken in an adiabatic container fitted with a movable frictionless adiabatic piston always operating at 1 atm . The gas A gets converted to gas B as per the reaction :

$3A\left(g\right)⟶2B\left(g\right),\mathrm{\Delta }H=-30\mathrm{kJ}/\mathrm{mole}$

If 75 % of A associates under the given conditions and initial temperature of the vessel was 300 K, then calculate the final temperature of the vessel.
[Given : $C_{\mathrm{P},\mathrm{A}\left(g\right)}=20\mathrm{J}/\mathrm{K}\text{ mole }$, $\left.C_{\mathrm{P},\mathrm{B}\left(g\right)}=30\mathrm{J}/\mathrm{K}\text{ mole }\right]$