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

75 : 63 :: 189 : 171 :: 55 : ?

45

75 : 63 :: 189 : 171 :: 55 : ?

The logic followed here is :

75 : 63

75 ⇒ 7 + 5 = 12

and 75 - 12 = 63

189 : 171

189 ⇒ 1 + 8 + 9 = 18

and 189 - 18 = 171

Similarly

55 :

55 ⇒ 5 + 5 = 10

and 55 - 10 = 45