To derive the raw material to purchase during an accounting period, an accountant would calculate the raw material required for production and then:

add the beginning raw-material inventory and subtract the desired ending raw-material inventory.
	add the beginning raw-material inventory and the desired ending raw-material inventory.
	add the desired ending raw-material inventory and subtract the beginning raw-material inventory.
	subtract the beginning raw-material inventory and the desired ending raw-material inventory.
	add the desired ending raw-material inventory and subtract both the beginning raw-material inventory and the expected units to be sold.