5. A shipping company wants to phase out a fleet of m (homogeneous) general cargo ships over a period of n years. Its objective is to maximize its cash assets at the end of the n years by considering the possibility of prematurely selling ships and temporary replacing them by charter ships. The company faces a known decreasing demands d d > > dn for ships in the n years respectively. Each ship earns a revenue of rk > 0 dollars in year k. At the beginning of year k, the company can sell any ship that it owns, accruing a cash inflow of sk> 0 dollars. If the company does not own sufficiently many ships to meet its demand, it must hire additional charter ships. The (net) cost of hiring a ship for the year k is hk > 0 after the deduction of the revenue Tk. The shipping company wants to meet its commitments and at the same time maximize the cash assets at the end of the year n. Formulate this problem as a min-cost TS