Question

A person who exercises vigorously several hours a day might take in about 22 m3 of air per day. A tree about 33 m tall and 0.55 m in diameter at its base produces about 84,000 L of oxygen per year. How many people, breathing as described this way, would five such trees supply with oxygen? (Please recall, that 1 m3 = 1000 L, and that normally there's about 20% of oxygen in the air around.)