Answer: Option (a) is the correct answer.
Explanation:
Using the Pythagoras theorem, we will calculate the the distance of
and
as follows.

= 24.17

= 22.56
Therefore, the path difference will be as follows.

= 24.17 - 22.56
= 1.61 m
Formula for constructive interference is as follows.

= 1.61 m (for n = 1)
Therefore, frequency will be calculated as follows.

= 
= 213.043 Hz
Thus, we can conclude that frequency produced by the speakers to create perfectly constructive interference is 213.04 Hz.