Perpetual inventory using FIFO

Beginning inventory, purchases, and sales for Item Zeta$9$ are as follows:

Oct. $1$ Inventory $200$ units at $$40$

Oct. $7$ Sale $180$ units

Oct. $15$ Purchase $180$ units at $$45$

Oct. $24$ Sale $150$ units

Assuming a perpetual inventory system and using the first$-$in$,$ first$-$out $($FIFO$)$ method, determine $($a$)$ the cost of goods sold o October $24$ and $($b$)$ the inventory on October $31.$

a$.$ Cost of goods sold on October $24$

b$.$ Inventory on October $31$