Which letter lies exactly midway between the letter seven places to the right of C and the letter four places to the left of X?

C stands at place 3, and seven places to its right is place 10, which is J. X stands at place 24, and four places to its left is place 20, which is T. The midpoint of 10 and 20 is 15, and the fifteenth letter is O. Taking the seventh to the right of C as I, at place 9 — counting C itself as the first step — gives a midpoint of 14.5 and so N; taking the fourth to the left of X as U, at place 21, gives 15.5 and so P; leaving X where it stands, at place 24, gives a midpoint of 17 and so Q.