
Answer:
0.2286  m,  0.686 m and  1,143 m
therefore we see that there is respect even where the intensity is minimal
Explanation:
Destructive interference to the two speakers is described by the expression
    Δr = (2n +1) λ/2
where r is the distance,  λ the wavelength and n an integer indicating the order of the interference
let's locate the origin on the left speaker
let's find the wavelength with the equation
    v =  λ f
     λ = v / f
we substitute
   Δr = (2n + 1) v / 2f
let's calculate for difference values ​​of n
   Δr = (2n +1) 343/(2 750)
   Δr = (2n + 1) 0.2286
we locate the different values ​​for a minimum of interim
  n   Δr (m)
   0   0.2286
   1   0.686
   2   1,143
therefore we see that there is respect even where the intensity is minimal