Twenty-seven people skated their hearts out at big Ben's birthday party at the skating rink last night, each producing an amazing 2,400 BTUs (British Thermal Units) of heat while listening to an hour's worth of Beatles, Spice Girls and Adele. The interior of the skating rink is 120 feet long, 35 feet wide and and 20 feet tall. To the nearest thousandth (3-decimal places), how many BTUs per cubic foot did they produce?