The correct interpretation of the function \( y = 120x + 30 \) is as follows:
- \( y \) is the total cost,
- \( x \) is the number of months,
- 30 is the one-time setup fee, and
- 120 is the monthly monitoring fee.
None of the provided options correctly represent this interpretation.
Based on the function, the proper understanding should be:
- \( y \) (total cost) increases by 120 for each month of monitoring after a setup fee of 30.
If there are any options that specifically reflect this meaning, those would be correct. However, since none fit, it appears the answer choices may not be accurate.