Option 3 is the right answer. Let us look into the meanings of the given words:
Forces: make (someone) do something against their will.
Rules: to exercise authority or power over.
Fixes: decides or settles on.
Guides: shows the way to others.
The given sentence is about a buffer stock and the committee that decides the quantity. So, the right word is 'fixes'. Complete sentence: The Cabinet Committee for Economic Affairs fixes the minimum buffer stock on a quarterly basis.