Simple completion question

[Zybomb]

In NL Hold Em, when faced with a bet (postflop), you should be folding or raising ___ % of the time.

If this varies table to table or opponent to opponent explain why

I understand the importance of a call (drawing hands, slow playing hands, questionable hands, etc) but how often should it be used and not used

Im focusing more on the actual flop here and somewhat on the turn (obviously on the river, a call can be used a lot more often)