$2\mathrm{kg}\text{ of ice at }-{20}^{\circ }\mathrm{C}$ is mixed with 5 kg of water at  20°C in an insulating vessel having a negligible heat capacity.  It is given that the specific heats of water and ice are  $1\mathrm{kcal}/\mathrm{kg}{/}^{\circ }\mathrm{C}\text{ and }0.5\mathrm{kcal}/\mathrm{kg}{/}^{\circ }\mathrm{C}$ respectively and the latent heat of fusion of ice is  $80\mathrm{kcal}/\mathrm{kg}.$Then