According to the meaning of the question, {36x7, x<9.

According to the meaning of the question, X should be 8, so the number of people for spring outing is 36× 8 = 288 (people).

(2) Scheme ①: The cost of renting 8 cars with 36 seats: 8× 400 = 3,200 yuan.

Scheme ②: The cost of renting seven 42-seat cars: 7× 440 = 3,080 yuan.

Scheme 3: As 42× 6+36× 1 = 288, the cost of renting six 42-seat and 1 36-seat cars is 6× 440+ 1× 400 = 3 040 (RMB).

Therefore, Scheme ③: Rent 6 vehicles with 42 seats, and 1 vehicle with 36 seats is the most economical.