customs authorities and customs duties

1. In international freight transport, a key role is played by the free-trade zones. In such areas, freight may be entered without the intervention of the customs authorities and customs duties are due only when the goods are moved outside. Get more more information on the free-trade zones through the Internet.
2. Formulate the minimum-cost flow problem for the Swiss NTN (see Section 6.2.2) intermodal carrier by knowing that the demand of containers in Milan and Madrid is 70 and 25, respectively. What is the optimal solution?