A one-time seasonal sales opportunity for a retail store for a product has a demand normally distributed demand with mean of 1000 and standard deviation 100. The cost of procuring the products from the supplier of the product is $40 per unit. The sales price of the product is $70. Any unsold units can be sold at a discounted price of $20. What is the optimal order quantity that minimizes the expected total understocking and overstocking costs?