Answer: 42*12 = 504
Step-by-step explanation: This question doesn't make alot of sense.
C=42*12 so C would = $504. The annual fee is $516 so a family paying by month would save $12 per year. However if they also had to pay the annual fee it would be C=42*12+504= $1020. The way the question was asked would be 504 however I am not sure it makes sense.