Difference between elements position in each set is following Fibonacci series that is 1,1,2,3,5,8 so on . B's position is 2 and A's position is 1 . K's position is 11 and J's position is 10 and the difference is 1 . E's position is 5 and C's position is 3 and the difference is 2 . same way last letters position difference must be 8 .