The lower surface of a slab of stone of face-area 3600cm^(2) and thickness 10cm is exposed to steam at `100^(@)C` . A block of ice at 0^(@)C rests on the upper surface of the slab. 4.8g of ice melts in one hour. Calculate the thermal conductivity of the stone. Latent heat of fusion of ice `=3.36xx10^(5) J kg^(-1)