Natural Gas Barbeque Please Please Help Me With My Chemistry Question!!! I Really Need Help :(!?

Please please help me with my chemistry question!!! i really need help :(!? - natural gas barbeque

I have no idea how to do this, please help: (

The question is:

Propane tank is used in remote areas of natural gas lines for cooking and heating, and is also the source of heat in most gas grills. Propane burns with oxygen through the balanced chemical equation:

C3H8 (g) + 5o2 (g) 3CO2 (g) + 4H2O (g)

Calculate the mass in grams of water vapor produced by burning 3.47 mole of propane.