MCTachyon

Sorry here is the rest of the question.
A fuel gas consists of 75% butane (C4H10), 10% propane (C3H8) and 15% butene (C4H8) by volume.
It is to be fed to the combustion chamber in 10% excess air at 25°C, where it is completely burnt to carbon dioxide and water. The flue gases produced are to be used to generate 5 bar steam from water at 90°C

I see you have been offering assistance on the following question. I am really struggling with this one and would appreciate any help you could offer.
Calculate:
The net calorific value (CV) per kmol of the fuel/air mix at 25°C?
Thanks,
Jon