I'm having hard time undestanding FIFO and LIFO. I don't exactly follow where these new units are coming from. And where did 102 units from Jan 13 came from this question? Thanks for the help

https://www.chegg.com/homework-help/questions-and-answers/fit-gym-began-january-merchandise-inventory-78-crates-vitamins-cost-total-4-290-month-fit--q26964071#:~:text=Transcribed%20Image%20Text-,Fit%20Gym%20began%20January%20with%20merchandise%20inventory%20of%2078%20crates,crates%20%40%20%24%20116%20each%20Jan.