One mole of an ideal monoatomic gas is kept in a rigid vessel. The vessel is kept inside a chamber whose temperature is 87∘C. Initially, the temperature of the gas is 4∘C. The walls of the vessel have an inner surface of area 500 cm2 and thickness of 2 cm. If the temperature of the gas increases to 8∘C in 5.0 seconds, find the thermal conductivity of the material of the walls.