I did #1, I just need help with #2 and #3

Required information Altira Corporation uses a perpetual inventory system. The following transactions affected its merchandise inventory during the month of August 2018: Aug.1 Inventory on hand-3,300 units; cost $7.40 each 8 Purchased 16,500 units for $6.80 each. 14 Sold 13,200 units for $13.30 each 18 Purchased 9,900 units for $6.20 each 25 Sold 12,200 units for $12.30 each 31 Inventory on hand-4, 300 units