Answer: 57 packages.
Step-by-step explanation: Just do 678 divided by 12 on a piece of paper or your calculator (or your head). The answer will be 57. You may ask, why? The answer is actually 56.5. Don't let B fool you. Since 56.5 is more than 56, B is wrong. However, you can take the remaining masks and store them in the 57th package. So C is correct.