On September 1, Stanton Supply had an inventory of 20 backpacks at a cost of $18 each. The company uses a perpetual inventory system. During September, the following transactions and events occurred: Sep. 3 Purchased 40 backpacks at $20 each from Janzen terms n/30. Received a 10% quantity discount. 6 Received credit of $72 for the return of 4 backpacks purchased on September 3 that were defective. 7 Paid for the September 3 purchase. 9 Sold 20 backpacks for $30 each to McGill Books terms n/30. 13 Cash sales of 15 backpacks for $30 each to Calvin Office Supply. 21 Purchased 25 backpacks at $18 each from Coleman Company terms 2/10, n/30. 30 A physical inventory count indicated an ending inventory balance of $774.