Ideal gas, PV $=$ nRT$,$ with the constant specic heat Cv$,$ undergoes an adiabatic expansion wherein its volume increases eightfold. Starting with the same pressure and volume as in the adiabatic process, the gas undergoes an isothermal expansion wherein its final pressure is $2^11/5$ times the final pressure and the final volume is half the final volume of the adiabatic process. Find the ratio $=$ Cp$/$Cv