In its first month of operations, Skysong, Inc. made three purchases of merchandise in the following sequence: $(1)220$ units at $$10,(2)440$ units at $$11,$ and $(3)420$ units at $$12.$

Assuming there are $140$ units on hand, compute the cost of the ending inventory under the $($a$)$ FIFO method and $($b$)$ LIFO method. Skysong uses a periodic inventory system.

$($a$)$ Cost of the ending inventory $$|||$

$($b$)$ Cost of the ending inventory $$|||$