An ultrasound device is used to measure blood flow in an artery. An ultrasonic transducer in the probe emits inaudible sound at f0 = 25 kHz. The sound enters the artery and reflects of moving blood cells. When the reflected sound returns to the probe it is combined with the emitted sound and fed to a speaker. The speaker produces audible sound at the beat frequency. The technician can listen to the speaker to better position the probe. If the technician holds the probe at an angle such that the blood is flowing directly away from the probe the speaker produces sound at fb = 200 Hz. Using this information and the fact that the speed of sound in blood is v = 1500 m/s, what is the velocity of the blood flow? (Answer 6.0 m/s) please provide equations and explanation.