One experimental method of measuring an insulating material's thermal conductivity is to construct a box of the material and measure the power input to an electric heater inside the box that maintains the interior at a measured temperature above the outside surface. Suppose that in such an apparatus a power input of 180 W is required to keep the interior surface of the box ${65}^{0}C$  above the temperature of the outer surface. The total area of the box is 2.18 m² and the wall thickness is 3.9cm. The thermal conductivity of material is  $x\times {10}^{-2}\frac{W}{mK}$. Find $x$ to nearest integer.