The officers of a high school senior class are planning to rent buses and vans for a class trip. Each bus can transport $70$ students, requires $3$ chaperones, and costs $$1,200$ to rent. Each van can transport $10$ students, requires$1$ chaperone, and costs $$100$ to rent. Since there are $770$ students in the senior class that may be eligible to go on the trip, the officers must plan to accommodate at least $770$ students. Since only $45$ parents have volunteered to serve as chaperones, the officers must plan to use at most $45$ chaperones. How many vehicles of each type should the officers rent in order to minimize the transportation costs?

A$.$ The officers should rent $?$ buses and $?$ vans to minimize the transportation costs.

B$.$ The minimal transportation costs are $?$