And if you make each bus - as a separate employee, in the card of this employee, write down the number of seats in the additional field,
1) create each trip as a separate process for an employee (bus), so you can see the number of trips planned for the week
2) each place that you sell is a product in the system, each sale is a sub-process from the trip process - i.e. the number of occupied seats is the sum of products in subprocesses (I think it can be counted as an action -
https://prnt.sc/u1nuou or
https://prnt.sc/u1nv75 ), the number of free seats is the difference between the total and the number of reserved
3) through the obligations of the client