Select the set in which the numbers are related in the same way as are the numbers ofthe following sets.(NOTE : Operations should be performed on the whole numbers, without breaking downthe 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 andthen performing mathematical operations on 1 and 3 is not allowed.)

(13, 26, 20)

(18, 31, 25)​​

Given: 

(13, 26, 20)

(18, 31, 25)

Logic: 1st number + 13 = 2nd number and 2nd number - 6 = 3rd number

For, (13, 26, 20)

13 + 13 = 26, 26 - 6 = 20

For, (18, 31, 25)

18 + 13 = 31, 31 - 6 = 25

Now, we check each options.

Option (a): (21, 34, 28) (Follow)

21 + 13 = 34, 34 - 6 = 28

Option (b): (37, 24, 18) (Not Follow)​

37 + 13 $$\neq$$ 24, 24 - 6 = 18​

Option (c): (14, 27, 33) (Not Follow)​

14 + 13 = 27, 27 - 6 $$\neq$$ 33​

Option (d): (15, 27, 21) (Not Follow)​

15 + 13 $$\neq$$ 27, 27 - 6 = 21​

Thus, correct option is (a).