During strenuous work a human body generates about 2,400 BTUs of body heat per hour. If 7 bodybuilders are in a gym that is 20 ft × 25 ft × 12 ft lifting weights, how many BTUs per cubic foot do they produce in 3 hours? (to the nearest tenth) A) 2.8 BTUs/ft3 B) 8.4 BTUs/ft3 C) 33.7 BTUs/ft3 D) 100.8 BTUs/ft3