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