Reduce by about 1/5 in order to support them.
6.8 billion people * 9 hectares per person = 61,200,000,000
61200000000 used /11.4 billion available = 5.38
This means we would be using 5.38 times more resources than we have, so we have to reduce by about 1/5 in order to get close to the available amount.