The body of a furnace is made of three layers. The inner side of the body is exposed to the heat of 800 C with the convection coefficient of 25 W/m2K and the inner wall temperature is 600 C. The conduction coefficient thickness of layer A is 20 W/mK and 0.3 m and the conduction coefficient thickness of layer C is 50 W/mK and 0.15 m. How mush should be the thermal conductivity of layer 2 if its thickness is 0.15 m. Note: temperature in outer wall is equal to the environment temperature (20 C) and the heat transfer is steady state.