How much does it cost to cross the sea by car?

The ferry for cars with less than 7 seats is 15 yuan, but I started the second ferry myself in September, 18, and I didn't care about paying for tickets at that time. After I went back, my wife and I had a long argument. It took me two days to learn that the original invoice of the ferry was 15 yuan, but the license plate number was not written. The key is that I am alone, but the invoice has been issued. I wonder if other riders have similar experiences with me?