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 a steady value at $-26^\circ\text{C}$. The thickness of the frozen 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 ice layer, at this instant would be given by