The inner and outer surfaces of a 25-cm-thick wall in summer are at 27°c and 35°c, respectively. the outer surface of the wall exchanges heat by radiation with the surrounding surfaces at 40°c, and convection with ambient air also at 40°c with a convection heat transfer coefficient of 8 w/m2·k. solar radiation is incident on the surface at a rate of 150 w/m2. if both the emissivity and the solar absorptivity of the outer surface are 0.8, determine the effective thermal conductivity of the wall. (round your answer up to 4 decimal places.) take σ