An square has an area of 29 in². In order to determine which of the given choises is the best estimate for the side of the square, you take into account that the are of a square is given by the square root of its side.
Then, the length of its side can be a number greater than 5 (because √25 = 5) and lower than 6 (because √36 =36). That is, due to 29in² is an area between 25in² and 36in², it is necessary that the side of the square is in between 5 and 6.
Hence, the answer is the first option