A company purchased 300 units for $30 each on January 31 . It purchased 400 units for $20 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. $7,500 B. $5,000 C. $250 D. $15,000