Thermodynamics (PV = nRT)

Here is the question:

A sample of propane placed in a closed vessel together with an amount of O2 that is 3.00 times the amount needed to completely oxidize the propane to CO2 and H2O at constant temperature. Calculate the mole fraction of each component in the resulting mixture after oxidation assuming that the H2O is present as a gas.

My work so far:

I balanced the equation

C3H8+ 5O2 --> 3CO2 + 4H2O

I know that the mole fraction is mole partial / mole total.

Mole partial would equal to 1, 5, 3, 4 respectively to the above equation.

I am having trouble with the mole total. How do you find it? The book says that that my mole total should be can this be?

Thanks for your help in advance!

Not too difficult
For each mole of C3H8 you need 5 moles of O2 but you have 3 times the amount of O2 needed (equivalent to 15 moles per mole of C3H8)
After reaction all of the C3H8 has gone, the equivalent of 10 moles of O2 are left and 3 moles CO2 and 4 moles H2O are made.
10 + 3 +4 = 17