Stuck on entropy problem after initial setup

[rbwang1225]

here's the problem http://picasaweb.google.com/RBWang1225/Thermodynamics#5412090936157167154

and this's my ideas http://picasaweb.google.com/RBWang1225/Thermodynamics#5412094345461831986

i don't know what's the next step.

 

[Redbelly98]

Welcome to physics forums. Please note, use the standard font and font size when posting here, unless there is good reason not to.

There is an error in your integral for Q, since

dQ = P dV, not dV/P​

on the isothermal paths.

Also, look up the relation between dS and dQ to help with calculating the entropy change.