An electric heater is used in a room of total wall area 137 m2 to maintain a temperature of 20∘C inside it when the outside temperature is −10∘C. The walls have three layers of different materials. The innermost layer is of wood of thickness 2.5 cm, the middle layer is of cement of thickness 1.0 cm and the outermost layer is of brick of thickness 25 cm. Find the power of the electic heater. Assume that there is no heat loss through the floor and ceiling. The thermal conductivities of wood, cement and brick are 0.125 W/m∘C, 1.5 W/m∘C and 1.0 W/m∘C respectively.