On average, a firm sells $2,500,000 in merchandise a month. Its cost of goods sold equals 60 percent of sales, and it keeps inventory equal to one-half of its monthly cost of goods on hand at all times. If the firm analyzes its accounts using a 360-day year, what is the firm's inventory conversion period? a. 30 days b. 15 days c. 20 days d. 360 days e. 10 days