A closed box is filled with dry ice at a temperature of -78.5 degrees C, while the outside temperature is 21.0 degrees C. The box is cubical, measuring 0.350 m on a side, and the thickness of the walls is 3..00 x 10^-2 m. In one day, 3.10 x10^6 J of heat is conducted through the six walls. Find the thermal conductivity of the material from which the box is made.