The thermal conductivity of an insulating material is found by casting a 0.1 m thick shell of the insulating material onto a hollow stainless steel sphere with an inner radius of 0.12 m and an outer radius of 0.15 m. An electrical heater located in the center of the stainless steel sphere is used to maintain the inner surface of the sphere at 230 oC. If 120 W are dissipated by the heater under steady-state conditions, what is the thermal conductivity of the insulation? Assume that the air temperature in the room is 25oC, the convection coefficient is 30 W/m2·K, and the conductivity of stainless steel is k=24 W/m·K.