How do I determine which inventory to record for sales returns according to LIFO and FIFO? -

For example,Dec 31 ending inventory 160 at $20Jan 2 purchase 100 at $22Jan 6 sale 180 at $40Jan 9 sale return 10 at $40For LIFO, after the sale there is 80 units at $20 left. For FIFO, after the sale there is 80 units at $22 left. For the sale return, which inventory is returned for FIFO? For LIFO? Is 10 units at $20 returned or 10 units at $22 returned?

Do the stuff actually have a shelf-life? Most will do FIFO because that s how inventory is actually moved.