Perpetual Inventory System and Inventory Costing Methods E6A. Refer to the data provided in E4A. 1. Using the perpetual inventory system, compute the cost of ending inventory, cost LO4 of goods sold, and gross margin. Use the average-cost, FIFO, and LIFO inventory costing methods. (Round unit costs to the nearest cent.) CCOUNTING CONNECTION Explain the reasons for the differences in gross mar gin produced by the three methods