Perpetual Inventory Using LIFO Beginning inventory, purchases, and sales data for prepaid cell phones for December are as follows: Inventory: Dec. 1 3,100 units at $39 Purchases: Dec. 10 1,550 units at $41 Dec. 20 1,395 units at $43 Sales: Dec. 12 2,170 units Dec. 14 1,860 units Dec. 31 930 units a. Assuming that the perpetual inventory system is used, costing by the LIFO method, determine the cost of goods sold for each sale and the inventory balance after each sale, presenting the data in the form illustrated in Exhibit 4. Under LIFO, if units are in inventory at two different costs, enter the units with the HIGHER unit cost first in the Cost of Goods Sold Unit Cost column and LOWER unit cost first in the Inventory Unit Cost column.