Perpetual inventory using LifO Beginning inventory, purchases, and sales data for prepaid cell phones for December are as follows: Inventory Dec. 12,200 units at $23 Sales Dec. 121,540 units 141,320 units 31660 units a. Assuming that the perpetual inventory systern is used, costing by the LFO 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 UFO, 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