Perpetual inventory using FIFO

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

Oct. $1$ Inventory $65$ units @ $$20$

Oct. $7$ Sale $47$ units

Oct. $15$ Purchase $61$ units @ $$23$

Oct. $24$ Sale $24$ units

a$.$ Cost of goods sold on October $24\backslash$lceil

b$.$ Inventory on October $31$