Concrete roof 8 m (+c 15 C 6 m 0.25 m The roof of an electrically heated home is 6 m long, 8 m wide, and 0.25 m thick, and is made of a flat layer of concrete whose thermal conductivity is k = 0.8 W/m C. The temperatures of the inner and the outer surfaces of the roof one night are measured to be 15C and 4C, respectively, for a period of 10 hours. Determine (a) the rate of heat loss through the roof that night and (b) the cost of that heat loss to the home owner if the cost of electricity is $0.08/kWh.