Beginning inventory, purchases, and sales for an inventory item are as follows: Assuming a perpetual inventory system and the last-in, first-out method: a. Determine the cost of goods sold for the September 30 sale. $ b. Determine the inventory on September 30 . $ Determine the amount to be paid in full settlement of each invoice, assuming that credit for returns and allowances was received prior to payment and that all invoices were paid within the discount period