Can someone help me with this question?

Question

Calculate the work for each of the following processes beginning with a gas sample in a piston assembly with T=305 K, P=1.79 atm, and V=4.29 (a) irreversible expensing against a constant external pressure of 1.00 atm to a final volume of 6.52 L; (b) isothermal, reversible expansion to a final volume of 6.52 L;

I understand that for a. the answer is -226 J. w=-p delta V => (-1.79atm*(6.52-4.29)*(101.325)). I do not understand how to get the answer for b.

Thank you!

Answer 1

Try -nRTln(V2/V1)