A jewelry firm buys semiprecious stones to make bracelets and rings. The supplier quotes a price of $8.30 per stone for quantities of 600 stones or more, $8.70 per stone for orders of 400 to 599 stones, and $9.20 per stone for lesser quantities. The jewelry firm operates 180 days per year. Usage rate is 35 stones per day, and ordering costs are $40. a. If carrying costs are $3 per year for each stone, find the order quantity that will minimize total annual cost. (Do not round intermediate calculations, except for order quantities which should be rounded to the nearest whole number. Round your final answer to the nearest whole number.)

b. If annual carrying costs are 25 percent of unit cost, what is the optimal order size? (Do not round intermediate calculations, except for order quantities which should be rounded to the nearest whole number. Round your final answer to the nearest whole number.)

c. If lead time is 4 working days, at what point should the company reorder? (Do not round intermediate calculations. Round your final answer to the nearest whole number.)