Radiant heating requirement, a shed is rectangular in shape, with the floor 15 ft by 30 ft and the roof 7.5 ft above the floor. The floor is heated by hot water running through coils. On cold winter days the exterior walls and roof are about -10°F. At what rate must heat be supplied through the floor in order to maintain the floor temperature at 75°F? (Assume that all surfaces of the system are black.