Hi Rohit,
We will solve this question with short method.
Given,
Speed of first car, Vs = 22 m/s
Speed of second car, Vo = 16.5 m/s
Frequency, f = 400 Hz
Velocity of Sound, V = 340 m/s
Now,
fA = f [ V + Vo / V - Vs ]
=> 400 [ 340 + 16.5 / 340 - 22 ]
=> 400 [ 356.5 / 318 ]
fA = 448 Hz Ans.
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