Ammonia has been studied as an alternative "clean" fuel for internal combustion engines, since its reaction with oxygen produces only nitrogen and water vapor, and in the liquid form it is easily transported. An industrial chemist studying this reaction fills a $100.L$ tank with $9\mathrm{.}6$mol of ammonia gas and $6\mathrm{.}8$ mol of oxygen gas, and when the mixture has come to equilibrium measures the amount of water vapor to be $6\mathrm{.}8$mol.

Calculate the concentration equilibrium constant for the combustion of ammonia at the final temperature of the mixture. Round your answer to $2$ significant digits.