Find the related number to complete the analogy: 5 : 18 :: 8 : ?

The first two numbers are related in a certain way. Choose the correct option to replace the question mark (?) having the same relationship with the third term. 7 : 81 :: 13 : ?

Choose one number which is similar to the numbers in the given set.
 Given set: 435, 147, 642, 192

Find the related number to complete the analogy: 5 : 18 :: 8 : ?

Select the set in which the numbers are related in the same way as are the numbers of the following sets.
(Note: Operations should be performed on the whole numbers, without breaking down the numbers into their constituent digits. E.g., 13 – Operations on 13 such as adding/subtracting/multiplying to 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)
(19, 31, 55)
(14, 26, 50)

Select the set in which the numbers are related in the same way as are the numbers of the following sets.
(NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into their constituent digits. E.g. 13 – Operations on 13 such as adding to/subtracting from/multiplying with 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)
(384, 32, 6)
(408, 68, 3)

In the following number-pairs, the second number is obtained by applying certain
mathematical operations to the first number. Select the pair in which the numbers are
related in the same way as are the numbers of the following pairs.
(Note: Operations should be performed on the whole numbers, without breaking down
the numbers into its constituent digits. E.g., 13 – Operations on 13 such as
adding/subtracting/multiplying etc. to 13 can be performed. Breaking down 13 into 1
and 3 and then performing mathematical operations on 1 and 3 is not allowed.)
108, 54
78, 39

In the following number-pairs, the second number is obtained by applying certain mathematical operation(s) to the first number. Select the number-pair in which the numbers are related in the same way as are the numbers of the following pairs.
(NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into their constituent digits. E.g. 13 – Operations on 13 such as adding to/subtracting from/multiplying with 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)
227, 112
240, 125

In the following number-pairs, the second number is obtained by applying certain mathematical operation(s) to the first number. Select the number-pair in which the numbers are related in the same way as are the numbers of the following pairs.
(NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into their constituent digits. E.g. 13 – Operations on 13 such as adding to/subtracting from/multiplying with 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)
18, 141
42, 165

Select the set in which the numbers are related in the same way as are the numbers of the following sets.
(NOTE: Operations should be performed on the whole numbers, without breaking down the numbers into their constituent digits. E.g. 13 – Operations on 13 such as adding to/subtracting from/multiplying with 13 can be performed. Breaking down 13 into 1 and 3 and then performing mathematical operations on 1 and 3 is not allowed.)
(11,18,396)
(19,12,456)