As with any combustion reaction, the products of combusting a hydrocarbon fuel (CxHyCxHy) with oxygen (O2O2) are carbon dioxide (CO2CO2) and water (H2OH2O). A mass of 13.49 gg for an unknown fuel was combusted in a reaction vessel containing an unknown amount of oxygen. At the end of the reaction, there still remained 13.47 gg of the fuel as well as 0.0327 gg of water and 0.0599 gg of carbon dioxide. The oxygen was completely consumed during the reaction. How many molecules of oxygen gas were initially present in the reaction vessel? Express the number of molecules to three significant digits.