Select the set in which the numbers are related in the same way as are the numbers of the given 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 /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)
(1, 6, 4)
(3, 15, 9)

(1, 6, 4)

(3, 15, 9)

Logic: (1st + 3rd)×2 - 3rd  = 2nd 
(1, 6, 4) =(1+4)×2-4 =10-4=6
(3, 15, 9)= (3+9)×2-9 =24-9=15
Lets check each options; 
(a) (10, 33, 11) = (10+11)×2 - 11 =21×2- 11 =42-11=31$$\neq$$33​
(b) (3, 18, 8 ) = (3+8)×2- 8 = 11 ×2 - 8= 22 - 8 = 16$$\neq$$18​
(c) (9, 25, 7) = (9+7)×2- 7 =16×2 - 7 = 32 -7 =25= 25 
Thus, the correct answer is (c) ​​