Answer:
f = 735 Hz
Step-by-step explanation:
given,
Person distance from speakers
r₁ = 4.1 m r₂ = 4.8 m
Path difference
d = r₂ - r₁ = 4.8 - 4.1 = 0.7 m
For destructive interference

where, n = 1, 3,5..
we know, λ = v/f

v is the speed of the sound = 343 m/s
f is the frequency

for n = 1

f = 245 Hz
for n = 3

f = 735 Hz
Hence,the second lowest frequency of the destructive interference is 735 Hz.