Heat transferred through the stone slab is used to melt the ice. According to the law of thermal conduction, the heat transferred $Q$ is given by: $Q = \frac{KA(\Delta T)t}{d}$ where $K$ is thermal conductivity, $A$ is area, $\Delta T$ is temperature difference, $t$ is time, and $d$ is thickness. Also, heat required to melt the ice is $Q = mL_f$, where $m$ is mass and $L_f$ is latent heat of fusion. Equating both expressions for $Q$: $\frac{KA(\Delta T)t}{d} = mL_f$ $K = \frac{m L_f d}{A(\Delta T)t}$ Substitute the given values: $m = 4.8\text{ kg}$, $L_f = 3.36 \times 10^5\text{ J/kg}$, $d = 0.1\text{ m}$, $A = 0.36\text{ m}^2$, $\Delta T = 100^{\circ}\text{C} - 0^{\circ}\text{C} = 100^{\circ}\text{C}$, $t = 1\text{ hour} = 3600\text{ s}$. $K = \frac{4.8 \times 3.36 \times 10^5 \times 0.1}{0.36 \times 100 \times 3600}$ $K = \frac{161280}{129600} = 1.24\text{ J/m/s/}^{\circ}\text{C}$