(b) A shopkeeper has a uniform demand of an item at the rate of 500 items per month. He buys from supplier at a cost of Rs. 8 per item and the cost of ordering is Rs. 30 for every order. The stock holding costs are 15% per year of stock value. Now, suppose the supplier offers a 5% discount on orders between 500 and 999 items including including these values and a 10% discount on orders exceeding or equal to 2500 . Find the optimal order quantity and associated minimum total cost