Please Explain how to get the solution

BE 8-7 Samuelson and Messenger (SAM) began 2021 with 200 units of its one product. These units were purchased near the end of 2020 for $25 each. During the month of January, 100 units were purchased on January 8 for $28 each and another 200 units were purchased on January 19 for $30 each. Sales of 125 units and 100 units were made on January 10 and January 25, respectively. There were 275 units on hand at the end of the month. SAM uses a periodic inventory system. Required: 1. Calculate ending inventory and cost of goods sold for January using FIFO. 2. Calculate ending inventory and cost of goods sold for January using average cost.