A 500-Hz Whistle Is Moved Toward a Listener at a Speed

Multiple Choice

A 500-Hz whistle is moved toward a listener at a speed of 10.0 m/s.At the same time,the listener moves at a speed of 20.0 m/s in a direction toward the whistle.What is the apparent frequency heard by the listener? (The speed of sound is 340 m/s. )

A) 473 Hz
B) 485 Hz
C) 533 Hz
D) 545 Hz