Beginning inventory, purchases, and sales for an inventory item are as follows:

Sep. $1$ Beginning Inventory $35$ units $$23$

$5$ Sale $20$ units

$17$ Purchase $37$ units $$25$

$30$ Sale $36$ units

Assuming a perpetual inventory system and the first$-$in$,$ first$-$out method, determine $($a$)$ the cost of the goods sold for the September $30$ sale and $($b$)$ the inventory on September $30.$

a$.$ Cost of goods sold $fill in the blank $1$

b$.$ Inventory, September $30$