[Curiosity, not homework] How do you compute the balance point for an asymmetrical hanging object?

This is a question for those types who do mathematical puzzles for fun (not I!). I do not have any use for the answer. I’m just curious about how you would solve this.

I have a picture calendar hanging on my wall. I suspend it not from the little punched holes but from a small metal clamp attached to the top (so the holes won’t tear). The clamp hangs over a nail. So I can position the clamp anywhere across the top. Normally I have it centered, and the calendar hangs straight.

Right now I have a large clamp attached to the lower left of the calendar page, holding an envelope with my November 29th opera tickets in it. So the calendar hangs crooked.

By moving the suspending clamp a little off center, I can straighten the calendar again.

What kind of formula describes the distance and direction off center that I have to move the top clamp so that the calendar hangs level once again with the extra weight on the lower left side?