I can't see how it'd be yours or anyone elses business.
I don't think I've ever asked the man hostage or him me... I'd answer if he did and we've talked about previous relationships but I just think it's a terribly crass question and not one that serves any real purpose to either party. One is likely to find it insulting and the other may be given something to worry about (if perhaps the number is higher than expected) that they can do absolutely nothing about... Seems daft to me.