The correct option is D 1500 Hz
Let ′O′ be the midpoint between S1 and S2.
Seperation between two sound sources S1S2=4.68 m
Path difference, Δx=|S1P−S2P|
From the data given in the question,
Δx=(√32+42−√42+1.682)=5−4.338≈0.66 m
Condition for constructive interference to occur,
Δx=nλ=n(vf) [where n=1,2,3,....]
⇒f=nvΔx=n×3300.66⇒f=500n Hz
For n=1 , f=500 Hz
For n=2 , f=1000 Hz
For n=3 , f=1500 Hz
and so on.
Thus, options (a), (b) and (d) are correct answers.