Options: more passengers, fewer passengers, number of seats, and rent.

Option 1 4 0 160 4000

Option 2 3 2 170 4500

Option 3 2 3 155 4250

Scheme IV 1 5 155 4750

Option 5 0 7 175 5250

Find out the rent of each scheme by tabular method, and get the most economical scheme 1.

That is, renting four buses.