Skysong's Boards sells a snowboard, Xpert, that is popular with snowboard enthusiasts. Information relating to Skysong's purchases of Xpert snowboards during September is shown below. During the same month, 121 Xpert snowboards were sold. Skysong's uses a perpetual inventory system. Date Explanation Units Unit Cost Total Cost Sept. 1 Inventory 23 HK$871 HK$ 20,033 Sept. 12 Purchases 45 916 41,220 Sept. 19 Purchases 20 937 18,740 Sept. 26 Purchases 44 945 41,580 Totals 132 HK$121,53