1. The problem statement, all variables and given/known data The task is to get Q, that gas has received through A-B-C change? Second task is to get usefulness of the machine? http://img40.imageshack.us/img40/8372/toplinaabc.jpg [Broken] 2. Relevant equations W=pV 3. The attempt at a solution If I use W=pV i get 0 from A->B so i cant get usefulness. No idea.