The topic is this: 23. A school organized 300 teachers and students to carry out social practice activities. The school plans to rent 8 Class A and Class B buses at the same time, but the company can only provide 6 Class A buses at most, of which Class A buses are limited to 45 people each and Class B buses are limited to 30 people each.

(1) Suppose you rent X buses of Class A, fill in the form with the algebraic expression containing X, and find out what kinds of car rental schemes the school has. And explain why.

(2) If car A rents 800 yuan/car and car B rents 600 yuan/car, which scheme is the most economical for school car rental? How much is the rent at this time?

(3) At present, the company can only provide seven buses with 60 seats, 45 seats and 30 seats, and the three buses rented by the school are just full. What kind of car rental plan does the school have?