Units Sold at Retail Date Description Units Purchased at Cost May 1 Beginning inventory 10 units @ $14 16 Purchase 40 units @ $17 22 Sales 28 Purchase 15 units @ $21 Assume Roberson's uses a perpetual inventory system. 30 units @ $25 Ending inventory Fill in the following charts with the balances on May 31: Inventory method Cost of goods sold LIFO FIFO Moving Average Cost