Trinity Bus Lines wants to maximize the number of passengers it can carry from Far Point to Newtown. Bus A can carry 60 passengers and costs $2,700 per month to run. Bus B can carry 48 passengers and costs $1,800 per month to run. The bus line has a maximum of 12 drivers, and can spend no more than $24,300 per month on running the buses. What is the maximum number of passengers they can carry, and which buses should they purchase? Formulate a linear programming model to solve this problem. List the extreme points and determine the solution graphically.