How many milliliters of O2 are consumed in the complete combustion of a sample of hexane, C6H14, if the reaction produces 789. mL of CO2?

How many milliliters of O2 are consumed in the complete combustion of a sample of hexane, C6H14, if the reaction produces 789. mL of CO2? Assume all gas volumes are measured at the same temperature and pressure. The reaction is 2C6H14(g) + 19O2(g) 12CO2(g) + 14 H2O(g)