In an electrically heated home, the temperature of the ground in contact with a concrete basement wall is 10.5 °C. The temperature at the inside surface of the wall is 24.9 °C. The wall is 0.12 m thick and has an area of 9.9 m2. Assume that one kilowatt · hour of electrical energy costs $0.15. How many hours are required for one dollar's worth of energy to be conducted through the wall?