An Airline company employing in total of 11 engineers, 15 pilots, and 21 stewards on a daily basis. The administration of the company is considering leasing two types of aircraft: the DM4 with a capacity of 25 passengers and the B77 with a capacity of 70 passengers. According to IATA regulations, the minimum staff requirements for each type of airplane is as follows:

Aircrafts Engineers Pilots Stewards

DM14 1 1 1

B77 1 2 3

a. Specify a linear programming model that determines the number of airplanes to be rented by the company to ensure the highest possible total passenger capacity. Present clearly the decision variables, the objective function and the constraints of the model.

b. Use the graphical solution method to solve the linear programming problem. Identify the optimal solution and the optimal value of the model.