Please formulate the following problem first, then use Excel Solver to solve it (You can simply follow the two videos: one for formulating and the other for solving). For submission purpose, please upload the Excel file.

Problem:

A school is preparing a trip for 400 students. The company who is providing the transportation has 10 buses of 50 seats each and 8 buses of 40 seats, but only has 9 drivers available. The rental cost for a large bus is $800 and $600 for the small bus. Formulate a linear programming model to determine how many buses of each type should be used for the trip for the least possible cost.