A hоme cаre pаtient whо uses оxygen continuously аt 4 L/min via NC has entered a pulmonary rehab program that has helped him increase his activities of daily living and has begun to get out of the house more often. He asks you how long he would be able to be out and about before his 8-lb liquid oxygen system will run out if his liquid oxygen tank shows 4-lbs. Which of the following would be correct?