How do you find the atomic mass/mass number of an atom

In the haber reaction, patented by german chemist fritz haber in 1908, dinitrogen gas combines with dihydrogen gas to produce gaseous ammonia. this reaction is now the first step taken to make most of the world's fertilizer. suppose a chemical engineer studying a new catalyst for the haber reaction finds that 671 liters per second of dinitrogen are consumed when the reaction is run at 271c and 0.99atm. calculate the rate at which ammonia is being produced. give your answer in kilograms per second. round your answer to significant digits.