A furnace wall is made up of three layers, one of fire-brick, one of insulating brick and one of red brick. The inner and outer surfaces are at 870°C and 40°C respectively. The respective coefficients of thermal conductivities of the layers are 1.0 (fire - brick), 0.12 (insulating brick) and 0.75 (red brick) Kcal / m-hr-°C and the thickness are 22 cm 7.5 cm and 11cm. Assuming close bonding of the layers at their interfaces. Calculate the rate of heat loss per sq. m per hour and the interface temperatures?