The inventory records for Radford Co. reflected the following: Beginning inventory @ May 1 800 units @ $3.20 First purchase @ May 7 900 units @ $3.40 Second purchase @ May 17 1100 units @ $3.50 Third purchase @ May 23 700 units @ $3.60 Sales @ May 31 2700 units @ $5.10 What is the amount of gross margin assuming the weighted average inventory cost flow method? (Round your intermediate calculations to two decimal places.) Select one: O a. $4050 O b. $4509 O c. $5400 d. $9720