MBO = 13,2,15 and first letter is 15 - 2 = 13 i.e. M ( no. in the 26 alphabets). FDJ = 6,4,10 and first letter is 10 - 4 = 6 i.e. F
SGZ = 19,7,26 and first letter is 26 - 7 = 19 i.e. S. Similarly,
?LW = ? ,10,21 and the first letter has to be 21 - 10 = 11 i.e. K, the 11th letter.
Hence K is the answer of this puzzle.