A company purchased 90 units for $20 each on January 31. It purchased 90 units for $30 each on February 28. It sold a total of 120 units. What is the amount of ending inventory, if the company uses the first-in, first-out inventory costing method? (Assume that the company uses a perpetual inventory system.) Select one: O a. $2700 O b. $1500 c. $1200 O d. Another amount e. $1800