Adiabatic Expansion Question

[Helen_Lee_1L]

In an adiabatic expansion, the volume goes from 1 Liters to 2.56 Liters at an external pressure of 1 atm. It releases 73J of heat at 1 atm, and returns to its original delta U. Find final volume.

So I understand that in an adiabatic expansion q=0, and so delta U equals work. Therefore, work (w) equals negative external pressure times delta volume. What would I have to do if I have to find the delta U if we are not give the energy?

[104733470]

Since there is no enthalpy, change in internal energy relies on work. and if external pressure is constant then work equales p times delta v (change in volume). Thats it. if pressure is not constant then work is nRln(v2/v1).