In an isothermal process the temperature is constant.
PV=nRT
So, it can be written that
PV=PA(8V)⇒PA=8P
In an adiabatic process,
PVγ=constant
γ for monoatomic gas is 35
So, it can be written
PPB=(8VV)35⇒PB=32P
Thus, the ratio of the pressures is
PAPB=8P32P=4