How to charge for the parking lot of Taiyuan Hubin International Hotel?

Taiyuan Hubin International Hotel parking lot is charged by the hour. According to relevant information, the free parking time in the parking lot of Taiyuan Hubin International Hotel is 20 minutes. If the actual parking time exceeds the free parking time, the free parking time will be included in the parking charging time, and if the parking time is less than one hour, it will be charged by one hour, and so on. The parking fee for small cars 1 hour is 3 yuan, and the parking fee for large cars 1 hour (inclusive) is 3 yuan, and the parking fee for large cars 1 hour is 5 yuan, and the parking fee for each increase 1 hour (inclusive) is 3 yuan. The maximum charge for a small car is 30 yuan, and that for a large car is 40.