Periodic Inventory by Three Methods The units of an item available for sale durina the vear were as follows: There are 1,500 units of the item in the physical inventory at December 31. The periodic inventory system is used. a. Determine the inventory cost by the first-in, firnt-out method. b. Dotermine the inventory cost by the lait.in, first out nethod. C. Determine the inventory cost by the weighted average cont method