Three identical units of merchandise were purchased during July, as follows:

Date Product Basic H Units Cost

July $3$ Purchase $1$ $$17$

$10$ Purchase $120$

$24$ Purchase $123$

Total $3$ $$60$

Average cost per unit $$20$

Assume one unit sells on July $28$ for $$30.$

Determine the gross profit, cost of goods sold, and ending inventory on July $31$ using the $($a$)$ first$-$in$,$ first$-$out, $($b$)$ last$-$in$,$ first$-$out, and $($c$)$ weighted average cost flow methods.