The correct interpretation of the function \( y = 99x + 15 \) is as follows:
- \( y \) is the total cost,
- \( x \) is the number of months of service,
- $15 is the one-time installation fee,
- $99 is the monthly service charge.
So, the correct statement that represents the meaning of each part of the function would be:
y is the total cost, x is the number of months of service, $15 is the installation fee, and $99 is the service charge per month.