salt and mineral (sam) began 2024 with 360 units of its one product. these units were purchased near the end of 2023 for $20 each. during the month of january, 180 units were purchased on january 8 for $23 each and another 360 units were purchased on january 19 for $25 each. sales of 170 units and 270 units were made on january 10 and january 25, respectively. there were 460 units on hand at the end of the month. sam uses a perpetual inventory system.