说明：  能实现计费功能。车起步开始计费，首先显示起步价（本次设计起步费为7.00元）,车在行驶3 km以内，只收起步价7.00元。车行驶超过3 km后,每公里2元，车费依次累加。当总费用达到或超过40元时，每公里收费4元。当遇到红灯或客户需要停车等待时，则按时间计费，计费单价为每20S收费1元
(Billing function can be realized. Start start charging car, the first show starting price (starting fee of this design is 7.00 dollars), car moving within 3 km, only charge the prices starting at 7.00 yuan. After the car traveled over 3 km, 2 yuan per km, the fare in turn accumulate. When the total cost, or more than 40 yuan, the per km charge 4 dollars. When a red light or stop waiting for customers when needed, according to the time of billing, billing unit price charged for each 1 per 20S)