#### Answer

a. 1 kg of $0^{\circ}C$ ice to $0^{\circ}C$ liquid water requires 80 kilocalories. This is discussed in the Check Point on page 331, item 3. This process is the reverse of the one described, using 1 kg instead of 1 gram.
b. Changing 1 kg $0^{\circ}C$ water to $100^{\circ}C$ water requires 100 kilocalories. This is discussed in the Check Point on page 331, item 2. This process is the reverse of the one described, using 1 kg instead of 1 gram.
c. Changing 1 kg $100^{\circ}C$ water to $100^{\circ}C$ steam requires 540 kilocalories. This is discussed in the Check Point on page 331, item 1. This process is the reverse of the one described, using 1 kg instead of 1 gram.
d. Changing 1 kg $0^{\circ}C$ ice to $100^{\circ}C$ steam requires the total of the above values, 80 + 100 + 540 = 720 kilocalories. This is discussed in the Check Point on page 331, item 4. This process is the reverse of the one described, using 1 kg instead of 1 gram.