Beginning inventory, purchases, and sales for an inventory item are as follows: Sep. 1 Beginning Inventory 28 units @ $18 5 Sale 16 units 17 Purchase 30 units @ $20 30 Sale 31 units Assuming a perpetual inventory system and the first-in, first-out method: a. Determine the cost of the goods sold for the September 30 sale. $ b. Determine the inventory on September 30. $