On October 1, a company received a contract to supply 6,000 units of a specialized product. The terms of contract require that 1,000 units be shipped in October; 3,000 Units in November and 2,000 units in December. The company can manufacture 1,500 units per month on regular time and 750 units per month on overtime. The manufacturing cost per item produced during regular time is Rs 3 and the cost per item produced during overtime is Rs 45. The monthly storage cost is Re 1. Formulate this problem as an LP model so as to minimize the total COS.