Can anyone explain this question for me please? I am still not sure how to do fifo, lifo and average.

thank you

E6-3 Mather sells a snowboard, EZslide, that is popular with snowboard enthusiasts. Below is information relating to Mathers purchases of EZslide snowboards during September. During the same month, 102 EZslide snowboards were sold. Mather uses a periodic inventory system Unit Total Cost Date lanationUnitsCost Sept. Inventory Purchases Purchases Purchases 12 $100 1,200 Sept. 12 Sept 19 Sept. 26 45 4,635 104 5,200 20 105 2,100 Totals 127 $13,135 Instructions Compute the ending inventory at September 30 and the cost of goods sold using the FIFO, LIFO, and average- cost methods. (For average-cost, round the average unit cost to three decimal places.) Prove the amount allocated to cost of goods sold under each method. Calculate inventory and cost of goods sold using FIFO, verage-cost, and LIEQ in a neriodic inuentoru sustem