Select the option that is related to the third term in the same way as the second term is related to the first term and the sixth term is related to the fifth term.

27 : 99 :: 21 : ? :: 13 : 43

75

Logic followed is:

(First number × 4) - 9 = Second number

27 : 99 

(27 × 4) - 9 = 108 - 9 = 99

13 : 43 

(13 × 4) - 9 = 52 - 9 = 43

Similarly,

21 : ? 

(21 × 4) - 9 = 84 - 9 = 75

So , 75 is correct answer .