Why is it not option A? (Doppler effect)Watch this thread
This is some what of a ratio proportion type concept.
speed= 340 ms-1
so 340/0.85f = wavelength
If f was 1.00 then the wavelength would have been 340 so the change in wavelength is 60 meters
Now speed = distance/ time
Distance is 60 meters time take is 1 second
so speed is 60 ms-1
Now if you notice the frequency has reduced from 1 to 0.85 so when frequency reduces and wavelength increase this would mean that the distance between the lady and the sound source has increased. Therefore the source of sound is moving away from her.