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.oC). The middle layer is made of fiberglass insulation with k = 0.04 W/(m.°C). The outside layer is 20omm thick and made of wood siding with k = 0.1 W/(m.oC). The inside temperature is 20°C, and the convection coefficient for the inside wall surface is hi = 40 W/(m2.oC). The convection coefficient for the outside wall surface is h0 = 70 W/(m2.oC). How thick must the insulation layer be so that the heat loss is no greater than 400 W if the outside temperature is -20°C?