You are inside a small (125 m3) laboratory, using liquid nitrogen at rate of 3 l/min from a large, insulated container. the liquid nitrogen expands as it evaporates, mixing with the air in the room (there is a fan that ensures that it is well-mixed), and all gases behave ideally. air leaves the room through a small crack in the door, such that the volume, pressure and temperature of the gas in the room all remain constant at 125 m3, 1 atm and 24°c, respectively. therefore, the mole fractions of nitrogen and oxygen are both time dependent. using the knowledge that the composition of normal air is 79% n2/21% o2, and that oxygen deprivation becomes a threat below 18% o2, calculate the maximum time (in minutes) that you can safely remain in the laboratory after starting the flow of nitrogen.