I do not understand how to organize this problem.

The following units of a particular item were available for sale during the calendar year: Jan 1 Inventory 8,000 units at $60.00 Feb 28 Sale 7,000 units April 30 Purchase 20,000 units at $65.00 17,000 units Aug 15 Sale Instructions: The company uses the weighted average cost method with a perpetual inventory system. Determine the cost of merchandise sold for each sale and the inventory balance after each sale