Using the FIFO inventory method, we assume that the units sold are the ones purchased first, and the ending inventory consists of the units purchased last. Therefore, the cost of goods sold for July would be calculated as follows:
- July 1 Beginning Inventory: 18 units at $19 = $342
- July 7 Purchases: 18 units at $19 + 18 units at $20 = $702
- July 22 Purchases: 9 units at $19 + 9 units at $20 + 12 units at $22 = $531
- Total Cost of Goods Available for Sale: $1575
- Cost of Goods Sold: 18 units at $19 + 12 units at $20 = $582
Therefore, the answer is C. $582.