In the letter series B, F, K, Q each letter is reached from the one before it by moving ahead through the alphabet by a step that grows by one each time — four places, then five, then six. Which letter comes next?

B is the 2nd letter; four ahead gives the 6th, F. Five ahead of F gives the 11th, K. Six ahead of K gives the 17th, Q. The next step is seven, and seven ahead of the 17th is the 24th letter, X. W (23rd) comes of repeating the step of six, Y (25th) of jumping eight, and V (22nd) of repeating the step of five.