Consider two containers A and B containing monoatomic gases at the same Pressure P , Volume V and…

In an isothermal process the temperature is constant.

$PV=nRT$

So, it can be written that 

$$\begin{gathered} PV=P_A\left(\frac{V}{8}\right) \\ \Rightarrow P_A=8P \end{gathered}$$

In an adiabatic process,

$P{V}^{\gamma }=$constant

$\gamma$ for monoatomic gas is $\frac{5}{3}$

So, it can be written

$$\begin{gathered} \frac{P_B}{P}={\left(\frac{V}{{\displaystyle \frac{V}{8}}}\right)}^{\frac{5}{3}} \\ \Rightarrow P_B=32P \end{gathered}$$

Thus, the ratio of the pressures is 

$\frac{P_B}{P_A}=\frac{32P}{8P}=4$$$$$