Some equations have been solved on the basis of certain system. Find the correct answer for the unsolved equation on that basis. If 98-39-27=31, 87-38-34=20, then 79-25-12 = ?
If the number 1 on the clock is replaced by the letter M, the number 2 is replaced by N and so on, then when the time is 21:00 p.m. the hour hand will be at ____ letter