Answer:
f = 632 Hz
Step-by-step explanation:
As we know that for destructive interference the path difference from two loud speakers must be equal to the odd multiple of half of the wavelength
here we know that
![\Delta x = (2n + 1)(\lambda)/(2)](https://img.qammunity.org/2020/formulas/physics/college/wqrz0uu93olnkrhuurv3qc8uy3zbkerayt.png)
given that path difference from two loud speakers is given as
![\Delta x = 5.80 m - 3.90 m](https://img.qammunity.org/2020/formulas/physics/college/8dxm0ib3i1rm0vxotuoxer6k2s4hsylcnt.png)
![\Delta x = 1.90 m](https://img.qammunity.org/2020/formulas/physics/college/udh0b9hyoy7gk8qpq5rl7pqoa83kh03ofo.png)
now we know that it will have fourth lowest frequency at which destructive interference will occurs
so here we have
![\Delta x = 1.90 = (7\lambda)/(2)](https://img.qammunity.org/2020/formulas/physics/college/oyuvlurrubl0kecv5oqxrjfond4ywol016.png)
![\lambda = (2 * 1.90)/(7)](https://img.qammunity.org/2020/formulas/physics/college/1pqxksaoo9k5i9fbzootvs66vbqvz5jggd.png)
![\lambda = 0.54 m](https://img.qammunity.org/2020/formulas/physics/college/hbuh6egy0bxijxccpo81ob2mintdin3ibu.png)
now for frequency we know that
![f = (v)/(\lambda)](https://img.qammunity.org/2020/formulas/physics/college/ezivdofqy9e2s0w93ntstmep2f3h7odaa6.png)
![f = (343)/(0.54) = 632 Hz](https://img.qammunity.org/2020/formulas/physics/college/z6t76ki5z8kp3c0mq60js26sfujcl7lirs.png)