A slab of stone of area of 0.36 ~m^2 and thickness 0.1 ~m is...

\begin{aligned} \frac{\delta Q}{\delta t} & =\frac{K A}{L}\left(T_1-T_2\right) \\ Q & =\frac{K A}{L}\left(T_1-T_2\right) t \\ Q & =m L_f \\ \frac{K A}{L}\left(T_1-T_2\right) t & =m L_f \\ K & =\frac{m L_f L}{A\left(T_1-T_2\right) t} \\ K & =\frac{4.8 \times 3.36 \times 10^5 \times 0.1}{0.36 \times 100 \times 3600} \end{aligned}\begin{aligned} & =\frac{4.8 \times 3.36}{0.36 \times 36} \\ & =1.24 \mathrm{~J} / \mathrm{m} / \mathrm{s} /{ }^{\circ} \mathrm{C} \end{aligned}