cost of sales is calculated by______. a. adding the cost of inventory on hand at the start of the period minus the cost of any purchases of materials during the year and then subtract the cost of ending inventory. b. adding the cost of the inventory at the start of the period plus the cost of any purchases of materials during the year and then subtract the cost of ending inventory. c. adding the cost of the inventory on hand at the start of the period plus the cost of any purchases of materials during the year and then add the cost of the Inventory. d. adding the cost of the inventory on hand at the end of the period plus the cost of any purchases of materials during the year and then subtract the costs of the beginning inventory