Can a book have more than one publishing place?

As an earlier poster said, write it as Boston-New York. In truth it shouldn't matter which one you put (Boston, New York or both) but I am aware there are some teachers out there who get maniacal about such things. I would suggest simply asking your professor. They won't mind, and that way you can work out exactly what they want. They will easily be able to see your problem and that it lists two publishing places and you are confused as to which one to write. But the general rule of thumb in academic writing like this, if in doubt, include all the available information. No one minds if you add too much information, but they do care if you don't have enough.