The walls of a refrigerator are typically constructed by sandwiching a layer of insulation between sheet metal panels. Consider a wall made of fiberglass insulation ( = 0.046 W m∙℃ ) and a thickness of 50mm. The sheet metal sandwiching the fiberglass is made of steel panels, each with a thermal conductivity of 60 W m∙℃ and a thickness of 3mm. If the wall separates refrigerated air at 4°C from the ambient air of the room of 25°C, what is the heat gain per unit surface area? Assume convection heat transfer coefficient for the inside and outside air are both 5 W m2∙℃ .