We apply Le' Chatelier's principle which states that any disturbance incurred to the equilibrium system shall be dealt such that the disturbance is countered to and attain equilibrium again. The equation is 4NH3 (ammonia) + 5O2 (oxygen) = 4NO (nitric oxide) + 6H2O (water). Increase in volume, decrease in pressure favors the forward reaction. Also, decreasing the amount of nitrous oxide and water favors the production of nitrous oxide as well.
