Hi. I don't know why I never thought of this before, but I'm questioning if I've been 3-betting correctly this whole time.

Let's say someone opens 3x BB (and let's assume a BB is $1 for simplicity's sake). When I want to 3 bet 2x the open, am I putting in $9 on top of villains $3 (to make the pot $12), or am I tripling the size of the pot to $9 by putting in $6?