6. The units that Cooper Products had available for sale during the year were as follows: Jan. 1 July 15 Sept 29 Inventory Purchase Purchase 36 units @ $25 $ 900 40 units @ $30 1,200 45 units 121 units @ $34 1,530 $3,630 There are 18 units of the product in the physical inventory at September 30. The PERIODIC inventory system is used. Determine the September 30 inventory cost using FIFO, LIFO, and weighted average cost: (a) FIFO (b) LIFO