how much weed can i expect growing

hey guys first time growing here i was wondering how much weed i can expect from having 6 plants under a 200 watt hps light with approriate temperature and humidity control

How long are two strings? That's kind of what you're asking. There is no way to predict what your yield will be because there are too many contributing factors. By the way, 200W would not be enough for 6 plants in my opinion. 2-3 plants, maybe, but not 6.