A company purchased 200 units for $20 each on January 31. It purchased 400 units for $30 each on February 28. It sold a total of 450 units for $90 each from March 1 through December 31 . If the company uses the last - in, first - out inventory costing method, calculate the cost of ending inventory on December 31. (Assume that the company uses a perpetual inventory system.) A. $150 B. $4,500 C. $10,500 D. $3,000