I've assumed that 6 development cards will get you 3 knights, a victory point, and 6 cards from the knights + Year of Plenty/Road Building/Monopoly cards, and subtracted these from the required production.
I've assumed that 6 development cards will get you 3 knights, a victory point, and 6 cards from the knights + Year of Plenty/Road Building/Monopoly cards, and subtracted these from the required production. YMMV.