Speedy Express is now operating 4 distribution centers which mainly serve 5 customer zones. Each customer zone receives all products from the same distribution once the assignment is made. The following table shows the four distribution centers and cost of delivery to each customer zone (in thousands of dollars).

	Zone A	Zone B	Zone C	Zone D	Zone E
DC1	20	58	52	65	18
DC2	11	42	20	50	52
DC3	40	16	51	68	19
DC4	10	21	29	77	37

1. If each distribution center can serve one customer zone only and each customer zone can be assigned to at most one distribution center, formulate the linear programming model for determining the assignment of distribution centers that will minimize the cost. (9 marks)

Speedy Express would like to change its business model. Now, it is necessary that each customer zone must be assigned to one distribution center, and each distribution center can serve more than one customer zone. However, to balance the workload, Speedy Express specified that distribution centers should not be assigned more than two customer zones. In addition, the assignment of DC2 to Zone C becomes infeasible under the new plan, formulate and solve the problem in Excel for determining the assignment of distribution centers that will minimize the cost and solve it using Solver.