A tank is initially filled with 100% (mole) CH₄ at 5 psig and 75 deg F. At time t>0, nitrogen is added to the tank at a rate of 150 lb_m/hr. If the tank is maintained at 5 psig and 75 deg F throughout the entire process, how long until the tan contents are at 5% (mole) CH₄. The gas can be treated as ideal. The volume of the tank is 200 ft³.