Need help figuring out cost of goods available and average cost

Riverbed Corp markets CDs of numerous performing artists. At the beginning of March, Riverbed Corp had in beginning inventory 2, 510 CDs with a unit cost of $7. During March, Riverbed Corp made the following purchases of CDs. During March 11, 860 units were sold. Riverbed Corp uses a periodic inventory system. (a) Determine the cost of goods available for sale. (b) Calculate Average Cost. The parts of this question must be completed in order. This part will be available when you compete the part above