I hear that the game is to exploit villain's frequency imbalance. But how do we determine villain frequencies? With hud stats right?

Like if villain has a 7% 3B tot, where a range of QQ+,AK is only 2.56%, so the other 4.5% could either but pure bluffs, or bluffs with Ace/King blocker, or JJ-99,AQ. how would you figure out what villains' 3b/fold, 3B/call, or 3B/5B ranges look like?

Tightness/looseness and aggressiveness is a good factor in determining how bluffy or strong range is for sure. What other factors are there? What can we do to turn these into numbers that we can plug into a math formula?

Side question:
vs 3B of 7%, is 4B AK for value or as semibluff?