A homeowner is considering these heating systems for heating his house: Electric resistance heating with $0.12/ kWh and 1 kWh 5 3600 kJ, gas heating with $1.24/therm and 1 therm 5 105,500 kJ, and oil heating with $2.3/gal and 1 gal of oil 5 138,500 kJ. Assuming efficiencies of 100 percent for the electric furnace and 87 percent for the gas and oil furnaces, determine the heating system with the lowest energy cost.