heat transfer Questions

A deep rectangular pond of surface area $A$, containing water (density = $\rho$, specific heat capacity = $s$), is located in a region where the outside air temperature is at a steady value of $-26^{\circ }\text{C}$. The thickness of the ice layer in this pond at a certain instant is $x$. Taking the thermal conductivity of ice as $k$, and its specific latent heat of fusion as $L$, the rate of increase of the thickness of the ice layer, at this instant, would be given by: