Select the option in which the two numbers are related in the same way as are the numbers in the given number-pair.

64 : 10 :: ?

In each set the sum of the digits in the first number will form the second number.
64 : 10

64 ==> 6+4 = 10

Option (a) 84 : 12

84 ==> 8+4 = 12

The above given logic is applicable here. So this is the correct answer.

Option (b) 54 : 12

54 ==> 5+4 = 9

The above given logic is not applicable here. So this is not the correct answer.

Option (c) 32 : 1

32 ==> 3+2 = 5

The above given logic is not applicable here. So this is not the correct answer.

Option (d) 42 : 8

42 ==> 4+2 = 6

The above given logic is not applicable here. So this is not the correct answer.