Answer:
Step-by-step explanation:
The former is the case of constructive interference and the later case relates to destructive interference.
For listener, path difference is the separation of loudspeaker as listener is not standing in between the speaker.
If λ be the wave length
For constructive interference
19 = n λ
For destructive interference
29 = (2n+1) λ / 2
= n λ + λ / 2
= 19 + λ / 2
10 = λ / 2
λ = 20 cm
= 0. 20 m