4. A cargo airline company in Central America ferries materials from four different airfields in Columbia (called A, B, C, and D) to three different airfields in Mexico (numbered 1,2, and 3). Requirements for airfield 1 are 1500 tons per year, 900 tons per year for airfield 2, and 1100 tons per year for airfield 3. The president of the airlines wants to determine how much material should be shipped from each airfield in Columbia to each airfield in Mexico so as to minimize total travel distance. Distances in kilometers between the airfields are as shown below: Distance (km) Annual Capacity (tons) Mexico 1 Mexico 2 Mexico 3 Columbia A 4125 4400 4200 1000 Columbia B 3400 3200 3125 1000 Columbia C 3800 3600 3500 700 Columbia D 4700 4500 4400 800 Annual Demand (tons) 1500 900 1100 The manufacturer wants to minimize transportation costs while meeting the requirement of each warehouse. a. What are the variables and what is the objective function for this problem? b. What are the constraints for this problem? C. Solve the problem using Excel Solver or LP Solve. What is the optimal transportation plan? (Hint: You should state how many tons should be shipped from each airport in Columbia to each airport in Mexico separately). d. What is the total travel distance travelled according to the colution?