A particular house wall consists of three layers and has a surface area of 30 m2. The inside layer is 10 mm thick and made of plaster board with a thermal conductivity of k = 0.2 W/(m. degree C). The middle layer is made of fiberglass insulation with k = 0.04 W/(m middot degree C). The outside layer is 20 mm thick and made of wood siding with k = 0.1 W/(m middot degree C). The inside temperature is 20degreeC, and the convection coefficient for the inside wall surface is k, = 40 W/(m2 middot degree C). The convection coefficient for the outside wall surface is ho = 70 W/(m2.degreeC). How thick must the insulation layer be so that the heat loss is no greater than 400 W if the outside temperature is -20degreeC?