A cars spare part company can use 3 different distribution warehouses (A, B, and C) for supplying its 4 main retailers (I-IV). Monthly transportation cost from each warehouse to each retailer is as follows: 

To maintain the warehouses the company faces fixed costs per month: 

Warehouse A: 6005 

Warehouse B: 9005 

Warehouse C: 7505 

Considering the given information, 

a) Formulate the extended) mathematical programming for such a problem to know which warehouses should be established and which customer is supplied by which warehouse in order to minimize the overall costs? It is supposed that each warehouse is able to support the demand of all the retailers. 

b) Either Apply the ADD-Algorithm or the Drop-Algorithm.

Retailers (i) IV A 850| 700 500 II III 1010 Warehouses B 980 530 740 C 540 580 1150 660 690