Nick's Camera Shop carries Zodiac instant print film. The film normally costs Nick $3.50 per roll, and he sells it for $5.50. Just assume Zodiac film has no shelf life. Nick's average sales are 21 rolls per week. His annual inventory holding cost rate is 25% and it costs Nick $20 to place an order with Zodiac. If Zodiac offers a 7% discount on orders of 400 rolls or more, a 10% discount for 900 rolls or more, and a 18% discount for 2000 rolls or more, determine Nick's optimal order quantity. Suppose The shop opens 280 days annually.