The formula for finding the area of a square that has a side length, s, is a=s^2.

To find the area of a square, use this formula-
A=a² where 'a' is the length of one side.
Since we know the area, and are trying to find the side length, then you would do the opposite-
a=√A
a=√40
√40≈6.32
The you would solve your other answers to compare. I started at the top, with choice one, and solved it this way-
2*√10
√10≈3.16
2*3.16≈6.32
So the answer would be choice 1, '2sqrt10'

B would have a negative result because 12-14 is -2