date	transaction	qty	price/cost
1-Jan	Beg Inv	1700	15
1-Feb	Purchase	2700	22
20-Feb	sale	3200	37
2-Apr	purchase	3700	28
4-Nov	sale	2900	40
calculate average cost per unit
Compute COGS assuming periodic system FIFO cost flow
Compute COGS assuming perpetual system FIFO cost flow
Compute COGS assuming periodic system LIFO cost flow
Compute COGS assuming perpetual system LIFO cost flow
Compute COGS assuming periodic system weighted-average cost flow
Compute COGS assuming perpetual system weighted-averag cost flow