A slab of stone of area 0.36 m2 and thickness 0.1 m is exposed on the lower surface to steam at 100°C. A block of ice at 0°C rests on the upper surface of the slab. In 56 minutes 4.8 kg of ice is melted. The thermal conductivity of slab is: (Given latent heat of fusion of ice= 3.36 x 105 J kg-1)