This question is better answered via experimentation. There is much more in rum than simply water and ethanol, and so while you might approximate it as a binary mixture, the truth of the matter is that each different brand and type of rum would have a different boiling point because the other species present in solution would vary from producer to producer. Approximating as a binary mixture with the rum being 40% alcohol (by volume), you would find a boiling point of around 83 degrees Celcius, however, that is almost certainly inaccurate.