Consider a square house 40 ft on a side, 10 ft high, with a flat roof on top and walls/roof that is 8 inches thick. The thermal conductivity for an un-insulated wall or roof is 1.6 W/Km, while with fiberglass insulation its 0.04 W/Km. Assume that the average internal temperature is balmy 70ºF and the external temperature is a chilly 0ºF. If we use electrical heating and the cost of electricity is $0.16 per kWh, calculate the amount of money you'd spend each month of heating in each case, and how much you'd save per month if you insulated the house.