\(PV =n R T=\text { constant }\)
\(P _1 V_1= P _2 V_2\)
\(PV = P _{ A }( V / 8)\)
\(P _{ A }=8 P\)
Adiabatic process, PV \(\gamma=\) constant \(\gamma\) for monoatomic gas is \(\frac{5}{3}\).
\(P _1 V _1^\gamma= P _2 V _2^\gamma\)
\(\frac{ P _{ B }}{ P }=\left(\frac{ V _1}{ V _2}\right)^\gamma=\left(\frac{ V }{ V / 8}\right)^{\frac{5}{3}}\)
\(P _{ B }=32 P\)
\(\frac{ P _{ B }}{ P _{ A }}=\frac{32 P }{8 P }=4\)