Brigham Young University:

Students attending BYU are required to follow an honor code, which mandates behavior in line with LDS teachings such as academic honesty, adherence to dress and grooming standards, and abstinence from extramarital sex and from the consumption of drugs and alcohol. Many students (88 percent of men, 33 percent of women) either delay enrollment or take a hiatus from their studies to serve as Mormon missionaries. (Men typically serve for two-years, while women serve for 18 months.) An education at BYU is also less expensive than at similar private universities, since "a significant portion" of the cost of operating the university is subsidized by the church's tithing funds.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". What do men typically spend 18 months doing?
unanswerable