5 is related to 27 by certain logic. Following the same logic, 7 is related to 51. To which of the following is 4 related, following the same logic? (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.)

5 is related to 27 by certain logic. Following the same logic 7 is related to 51.

5: 5 × 5 + 2 = 27

7: 7 × 7 + 2 = 51

Similarly, 

4: 4 × 4 + 2 = 18

Therefore, the answer is 18. ​​