$1.56\times {10}^5 \mathrm{J}$ of heat is conducted through is $2 {\mathrm{m}}^2$ wall of $12 \mathrm{cm}$ thick in one hour. The temperature difference between the two sides of the wall is $20 \mathrm{℃}$. What is the thermal conductivity of the material of the wall (in $\mathrm{W} {\mathrm{m}}^{-1\mathrm{ }}{\mathrm{K}}^{-1}$)?