One mole of monatomic ideal gas is contained in a rigid container of volume V with walls of total surface area A, thickness x and thermal conductivity K. The gas is at an initial temperature To and pressure Po. The temperature of the surrounding air is Ts. All the temperatures are in absolute scale. If the temperature of the gas at any time t can be expressed as T(t)=Ts−(Ts−To)e−λt, find the value of λ.