Christina sells beauty supplies. Her annual demand for a particular skin lotion is 1,000 units. The cost of placing an order is $20, while the holding cost per unit per year is 10 percent of the cost. This item currently costs $10 if the order quantity is less than 300. For orders of 300 units or more, the cost falls to $9.80. To minimize total cost, how many units should Christina order each time she places an order