Answer
See explanation.
Work Step by Step
The person is approaching the sound source in the front, and will perceive a higher frequency than what is emitted.
At the same time, the person is walking away from the sound source in the back, and will perceive a lower frequency than what is emitted.
If both sources are emitting the same frequency, this means the person will perceive the 2 sources as being out of tune with one another.
