At the beginning of its operations in March 2020, Mastiff Supplies Ltd. began with 7,380 units of inventory that it purchased at a cost of $6.90 each. The company's purchases during March were as follows: March 13 Sales during March: 4,920 units @ $7.80 March 2 4,920 units March 20 2,760 units Mastiff Supplies uses a perpetual inventory system