A furnace wall is composed of three layers, 30 cm of firebrick (k=1.560 W/mK), followed by 23 cm of kaolin insulating brick (k=0.073 W/mK), and finally 5 cm of masonry brick (k=1.0 W/m* K). The temperature of the inner wall surface is 1370 K and the outer surface is at 360 K. Assume the cross-section area is 1 m2.

Find the thermal resistances R1 in (W/K)