A jewellery firm buys semi precious stones to make bracelets and rings. The supplier quotes a price of $8 per stone for quantities of 600 stones or more, $9 per stone for orders of 400 to 599 stones, and $10 per stone for lesser quantities. The jewellery firm operates 200 days per year. Usage rate is 25 stones per day, and ordering costs are $48 i) If carrying costs are $2 per year for each stone, find the order quantity that will minimize total annual cost