Aballet class of 10 dancers uses a discarded shipping container as a temporary classroom. the walls, floor, and roof of the container are made of the same uniform material, and the container measures 10 feet x 10 feet x 30 feet. on a day when the air temperature is 30°f and the ground temperature is 40°f, determine the minimum r-value of the container in order to maintain a constant interior temperature of 65°f. assume each of the 10 dancers outputs 600 btu/hr of metabolic heat and no additional heat source is available.