Select the option 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 its constituent digits. E.g. 13 - Operations on 13 such as adding/deleting /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)

(7, 1, 3)
(12, 2, 5)

In each set, the difference between the first and second numbers is divided by 2 to obtain the third number.

(7, 1, 3) ==> Third number = $$\frac{\left(7-1\right)}{2}$$ = $$\frac{\left(6\right)}{2}$$ = 3
(12, 2, 5) ==> Third number = $$\frac{\left(12-2\right)}{2}$$ = $$\frac{\left(10\right)}{2}$$ = 5

Option (a) (30, 8, 11)

Third number = $$\frac{\left(30-8\right)}{2}$$ = $$\frac{\left(22\right)}{2}$$ = 11

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

Option (b) (26, 4, 20)

Third number = $$\frac{\left(26-4\right)}{2}$$ = $$\frac{\left(22\right)}{2}$$ = 11

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

Option (c) (32, 6, 18)

Third number = $$\frac{\left(32-6\right)}{2}$$ = $$\frac{\left(26\right)}{2}$$ = 13

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

Option (d) (40, 10, 30)

Third number = $$\frac{\left(40-10\right)}{2}$$ = $$\frac{\left(30\right)}{2}$$ = 15

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

Hence option (a) is the correct answer.