X$-$cell Inc. made purchases of a particular product in the current year as follows :

Ending inventory consists of $320$ units, specifically identified as follows :

$90$ units from beginning inventory

$20$ units from the March $4$ purchase

$210$ units from the May $7$ purchase

Assuming a periodic system, determine the costs to be assigned to cost of goods sold and ending inventory using the following systems :

a$.$ FIFO

b$.$ LIFO

c$.$ Weighted Average

d$.$ Specific Identification.