Periodic Inventory Using rifo, Liro, and Weighted Average Cost Methods The units of in ifent avalable for sale during the year were as follows: There are 20 unas of the item in the physical inventory st December 31. The periodic inventory system in used. Detemine the inventory cost using (a) ihe first-in, linst out (riro) method: (b) the last-in, first out (Uro) method; and (c) the weohted averoge cost method (Ptound per unit cost to two decimal placrs and your final answer to the neare whole dottar). a. Finstin, frat - out (rifo)