According to the transparency how is nitrogen returned to the atmosphere

According to transparency, nitrogen is returned to the atmosphere through a process called denitrification.

The process goes as follows:
Ammonification: This occurs when the decomposers break down the the wastes of the organisms and release the nitrogen that these organisms contained in the form of ammonia
Nitrification: This occurs when the ammonia is oxidized into nitrites which further oxidize into nitrates by the bacteria in the soil
Denitrification: This occurs when anaerobic bacteria break down these nitrates, thus, producing nitrogen into the atmosphere.

You would do 1500/4 and the answer is 375