The company "World Airline System" is composed of the routes X and Y, and each route requires 10 aircrafts. These routes can be serviced by three types of aircrafts ? A, B, and C. There are (five) 5 type A aircraft available, 10 type B, and 10 type C. These aircrafts are identical except for their operating costs, which are as follows:

Annual operating cost ($ millions)