7 kg of ice at 0◦C is converted to steam at 100◦C. How much heat is needed? The heat of fusion for water is 79500 cal/kg, its heat of vaporization is 5.4 × 105 cal/kg, and its speciﬁc heat is 1000 cal/kg ·◦C. Answer in units of kcal.
What is the formula that I am supposed to use?