It is given that displacement of piston be in final state $x$ and if $A$ is the area of cross-section of the piston. 

Hence the final volumes of the left and right part finally can be given by figure as 

${V_L} = \frac{{{V_0}}}{2} + Ax$ and ${V_R} = \frac{{{V_0}}}{2} - Ax$ 

As it is given that the container walls and the piston are adiabatic in left side and the gas undergoes adiabatic expansion and on the right side the gas undergoes adiabatic compressive. 

Thus we have for initial and final state of gas on left side 

${P_1}{\left( {\frac{{{V_0}}}{2}} \right)^\gamma } = {P_f}{\left( {\frac{{{V_0}}}{2} + Ax} \right)^\gamma }$                      ..... $(i)$ 

Similarly for gas in right side, we have ${P_2}{\left( {\frac{{{V_0}}}{2}} \right)^\gamma } = {P_f}{\left( {\frac{{{V_0}}}{2} - Ax} \right)^\gamma }$                            ..... $(ii)$ 

From eq. $(i)$ and $(ii)$ 

$\frac{{{P_1}}}{{{P_2}}} = \frac{{{{\left( {\frac{{{V_0}}}{2} + Ax} \right)}^\gamma }}}{{{{\left( {\frac{{{V_0}}}{2} - Ax} \right)}^\gamma }}}$ ==> $Ax = \frac{{{V_0}}}{2}\frac{{\left[ {P_1^{1/\gamma } - P_2^{1/\gamma }} \right]}}{{\left[ {P_1^{1/\gamma } + P_2^{1/\gamma }} \right]}}$

Now from equation $(i)$ 

${P_f} = \frac{{{P_1}{{\left( {\frac{{{V_0}}}{2}} \right)}^\gamma }}}{{{{\left[ {\frac{{{V_0}}}{2} + Ax} \right]}^\gamma }}}$