Ritter states that space technology that seemed futuristic in the 1950s has long since been invented (16). what does the number 16 refer to?

If you had attached some options to choose I would definitely have helped you and give the correct answer. Even though this excerpt looks like a  paragraph 16 in the research paper but I am pretty sure that the right answer is page 16 of a book by author Ritter. Because the number at the end always indicates a page number on which the quote can be found. Do hope you still need the answer because this one is really helpful.