Periodic Inventory System and Inventory Costing Methods In chronological order, the inventory, purchases, and sales of a single product for a recent month are as follows: Units Amount per Unit June 1 Beginning inventory 150 $ 60 4 Purchase 400 66 12 Purchase 800 72 16 Sale 1,300 120 24 Purchase 300 78 Using the periodic inventory system, compute the cost of ending inventory, cost of goods sold, and gross margin. Use the average-cost, FIFO, and LIFO inventory costing methods. Explain the differences in gross margin produced by the three methods. Round unit costs to cents and totals to dollars.