Answer:
The third lowest frequency is 1489.27 Hz.
Explanation:
Given that,
Distance of person from one speaker= 4.50 m
Distance of person from the other = 3.80 m
The longest wavelength is the shortest frequency.
We need to calculate the difference between the speakers
The difference between the speakers d= 4.50-3.80 =0.7 m
We know that,
The longest wavelength is such that one wavelength

So, The third longest wavelength is

Put the value of d


We need to calculate the lowest frequency
Using formula of frequency



Hence, The third lowest frequency is 1489.27 Hz.
Firstly, do you understand the concept of a Wavelength? If not i can tell you?
North east would be the answer