2 kg of ice at −20∘C is mixed with 5 kg of water at 20∘C in an insulating vessel having a negligible heat capacity. Calculate the final mass of water remaining in the container. It is given that the specific heats of water & ice are 1 kcal/kg∘C & 0.5 kcal/kg∘C while the latent heat of fusion of ice is 80 kcal/kg
a. 7 kg
b. 6 kg
c. 4 kg
d. 2 kg