How much should i write?

I am an international students from Hong Kong (it does not belong to China). I gonna take both macro and microeconomics this year. But i dont know how much to write in the free respond part.
We usually do a whole paragraph explaining the sub-sub-question here in Hong Kong. But in the past papers from college board, it seems that it is not necessary coz the answer from the scoring guides are sooooo short (to me)…</p>