Samuelson and Messenger (S&M) began 2016 with 350 units of its one product. These units were purchased near the end of 2015 for $24 each. During the month of January, 250 units were purchased on January 8 for $27 each and another 300 units were purchased on January 19 for $29 each. Sales of 160 units and 250 units were made on January 10 and January 25, respectively. There were 490 units on hand at the end of the month. S&M uses a periodic inventory system