1. Five warehouses are supplied by four factories. The supply available from each factory, the demand at each warehouse and the cost per unit of transporting goods from the factories to the warehouses are summarised in the following table: W1 W2 W3 W4 W5 Supply F1 13 9 15 10 12 40 F2 11 10 12 12 9 10 F3 12 9 11 12 9 20 F4 13 12 13 12 10 10 Demand 12 15 20 15 18 Use the North-West Corner method to find an initial basic feasible solution of this problem. Find the optimal solution of this problem, i.e. the solution that minimises the transportation costs, clearly showing and explaining your working.