In 2023, Matador Company switched its inventory method from average cost to FIFO. Inventories at the end of 2022 were reported in the balance sheet at $55 million. If the FIFO method had been used, 2022 ending inventory would have been $50 million. Ignoring the effect of income taxes, the adjustment to 2023's beginning retained earnings would be: a. $0 b. $50 million increase c. $5 million increase d. $5 million decrease