How can I compute cost of goods available for sale?

Marlow Company uses a perpetual inventory system. It entered into the following calendar year 2011 purchases and sales transactions. Date Activities Units Acquired at Cost Units Sold at Retail 600 units @ $44/unit 200 units @ $40/unit 100 units @ $20/unit . Jan. Feb. 10 Mar. 13 Mar. 15 Aug 21 Sept. 5 Sept. 10 Beginning inventory Purchase... Purchase.... Sales ... Purchase...... Purchase. Sales. 400 units @ $75/unit . 160 units @ $60/unit 280 units @ $48/unit 200 units @ $75/unit 600 units 1.340 units Required 1. Compute cost of goods available for sale and the number of units available for sale