The correct interpretation of the function \( y = 15x + 12 \) in the context of the gym's charges is as follows:
- \( y \) represents the total cost.
- \( x \) represents the number of months someone is a member of the gym.
- The term \( 15x \) indicates that for each month of membership, there is a charge of $15.
- The term \( 12 \) represents the one-time enrollment fee.
Thus, the correct statement is:
y is the cost and x is the number of months someone is a member of the gym; $12 is the enrollment fee and $15 is the monthly fee.