15. OC Incorporated had an average receivables collection period of 19 days in 2020. Galambos has stated that it wants to decrease its collection period in 2021 to match the industry average of 15 days. Credit sales in 2020 were $300 million, and analysts expect credit sales to increase to $400 million in 2021. To achieve the company's goal of decreasing the collection period, the change in the average accounts receivable balance from 2020 to 2021 that must occur is closest to:

a. $420,000.

b. $420,000.

d. $836,000.