TNK Ltd uses the periodic inventory system and had the following inventory information available: Units Unit Cost Jan. 1 Opening inventory 4 Mar. 8 Purchase 30 5 Jul. 29 Purchase 40 6 Nov. 4 Purchase 20 8 100 10 A physical count of inventory on December 31 revealed that there were 30 units on hand. Required: Compute the cost of closing inventory under first in, first out (FIFO) method