A source is moving with constant speed vs=20 m/s towards a stationary observer due east of the source. Wind is blowing at the speed of 20 m/s at 60∘ north of east. The source has frequency 500 Hz. Speed of sound = 300 m/s. The frequency registered by the observer is approximately
a. 541 Hz
b. 552 Hz
c. 534 Hz
d. 517 Hz