An observer stands 23.1 meter behind marksman practicing at a rifle range. The marksman fires the rifle horizontally, the speed of the bullets is 831.6 m/s, and the air temperature is 20 degree Celsius. Calculate how far does each bullet travel before the observer hears the report of the rifle? Suppose that the bullets encounter no obstacles during this interval, and neglect both air resistance and the vertical component of the bullets' motion.