How do i find the answer on task b)?

Problem 3: We have a transportation problem with two stocks and five customer districts. Both stocks have a capacity of 2000 units and the customer's demand is given as the vector D: D = [500, 700, 600, 1000, 400] The unit costs by transporting from stock to customer is shown in matrix A: District 1 District 2 District 3 District 4 District 5 Stock 1 12 15 20 18 14 Stock 2 10 16 13 19 17 a) Find the optimal solution to the transportation problem, and make a sketch of the solution. The two stocks in problem a is served by two factories. Factory 1 has a production capacity of 2000 units and factory 2 has a production capacity of 1500 units during the time horizon. The unit costs for transportation from factory to stock is shown in the matrix: Stock 1 Stock 2 Factory 1 5 8 Factory 2 7 6 b) Formulate a transshipment model for the distribution problem and find the optimal solution. Make a sketch of the solution and compare it with the result from problem a. In problem b, it is not allowed with direct transportation from factories to districts. If this possibility should be included in the model, we also need the unit costs for transportation directly from factories to customer districts. These costs are shown in the matrix below