Choose the option in which the third pair of letters is related to the second pair in the same way as the second pair is related to the first pair:27 : 9 :: 64 : ?

Choose the option in which the third pair of letters is related to the second pair in the same way as the second pair is related to the first pair:
विकल्प का चयन करें जो तीसरे अक्षर युग्म उसी तरह संबंधित है जैसे दूसरा अक्षर युग्म पहले अक्षर युग्म से संबंधित है|
27 : 9 :: 64 : ?