Periodic Inventory by Three Methods The units of an item available for sale during the year were as follows: 18 units $33 Jan. 1 Inventory Feb. 17 Purchase 18 units $35 Jul. 21 Purchase 17 units $38 Nov. 23 Purchase 19 units $39 There are 18 units of the item in the physical inventory at December 31. The periodic inventory system is used. Round average unit cost to the nearest cent and final answers to the nearest whole dollar, if required. a. Determine the inventory cost by the first-in, first-out method. b. Determine the inventory cost by the last-in, first-out method. c. Determine the inventory cost by the weighted average cost method.