A laboratory furnace wall is constructed of 0.20m thick fireclay brick having k1=1.2 W/m-°C. This is covered on the outer surface with a 0.035 m thick layer of insulation material having k2 =0.08W/m -°C .The furnace inner brick surface is at 980°C and the outer surface of the insulation material is at 35°C . Calculate the interfacial temperature between the brick and the insulation.