4. The units of an item available for sale during the year were as follows: Jan. 1 Inventory 30 units @ $102 Mar. 10 Purchase 70 units @ $112 Aug. 30 Purchase 30 units @ $116 Dec. 12 Purchase 70 units @ $120 There are 80 units of the item in the physical inventory at December 31. The periodic inventory system is used. a. Determine the ending inventory and the cost of merchandise sold by three methods. b. If units were sold for $180 each, what is the gross profit under all three methods. 5. The units of an item available for sale during the year were as follows: January 10 Inventory 27 units @ $90 February 27 Purchase 54 units @ $98 July 11 Purchase 63 units @ $106 November 13 Purchase 36 units @ $115 There are 50 units of the item in the physical inventory at December 31. The periodic inventory system is used. Determine the ending inventory cost by (a) the first-in, first-out method, (b) the last-in, first-out method, and (c) the average cost method