The units of an item available for sale during the year were as follows.

Jan. 1 Inventory 54 units at $1,200

Mar. 6 Purchase 108 units at $1,380

July 14 Purchase 126 units at $1,560

Nov. 2 Purchase 112 units at $1,650

There are 90 units of the item in the physical inventory at December 31. The periodic inventory system is used. Determine the inventory cost by (a) the First-in, First-out method, (b) the last-in, first-out method, and (c) the average cost method.