A group of anthropologists is staying in the high Arctic for a month, and they need accommodation. They are directed to a small company, Inuit Igloos. "How thick do you want the walls?" asks Inuk, the head igloo maker. After some conferring, they reply that it should be 20^oC inside when the temperature is 20^oC outside. After looking the anthropologists over and poking them a bit, Inuk estimates that they would give off 38 MJ of heat per day. If the inside radius of the hemispherical igloo is to be 2 m, and the thermal conductivity of the compacted snow is 0.209 W/m ∙ K, how thick should the walls be? (As an approximation, assume that the inner surface area of the igloo is equal to the outer surface area.)