Question of the week 25-Mar-2020

Q) The value of "X" in the below image is

a) √61       b) √71          c) √81        d) None of these 

It is a question to trap you. Previous question here. Next week question here. It is solvable in less than 45 seconds provided you know the trick that i will be discussing in the book. Your answer only with a logical explanation is welcomed in the comments section.