At a college party 5 girls are sitting in a row. P is to the left of M and to the right of O. R is sitting to the right of N, but to the left of O. Who is sitting in the middle?
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 = ?