Hi guys, I've been working on this problem for so long but I cannot figure out how to approach it...what am I supposed to do? Here is the question, and what I have tried...

(Background info is included so you know what's going on...)

What I've done: b) I've taken the derivative of the van der Waals gas equation to get 2a/v^3 - RT/(v-b)^2

Thanks so much to anyone that can help!