Select the option that is related to the third number in the same way as the second number is related to the first number and the sixth number is related to the fifth number.

16 : 20 :: 256 : ? :: 49 : 56

272

16 : 20 :: 256 : ? :: 49 : 56

The  logic followed here is :

ROOT OF IST NUMBER : IST NUMBER² + IST NUMBER = IIND NUMBER

AS

ROOT OF 16 :

4² + 4 = 20

AND

ROOT OF 49 :

7² + 7 = 56

SIMILARLY

ROOT OF 256 :

16² + 16 = 272