I am not sure what assumption I can make for this problem and why it's valid. It certainly isn't isochoric. Since the volume changes, I conclude its not isobaric either (P should decrease). I don't think it's adiabatic because the part (b) clearly hints that it is not reversible in part (a). That leaves me with isothermal. But if a gas expands, it's temperature should decrease. Therefore, I don't know which of these processes I could use to solve for the final temperature.