The following units are available for sale during the year:
January 1 Beginning inventory 10 units at $18 each
April 3 Purchase 30 units at $20 each
August 31 Purchase 28 units at $28 each
September 29 Purchase 17 units at $30 each
December 31 Ending inventory 21 units
Determine ending inventory cost by (a) FIFO method, (b) LIFO method, and (c) average cost method