A speaker which produces a frequency of 312 Hz is moving away from an observer and towards a wall at 3 m/s when it is 30 degrees Celsius. What is the frequency of the sound that travels directly to the observer? What is the frequency of the sound that bounces off the wall and then gets to the observer? How many beats per second are heard by the observer?

FIRST QUESTION: f2=312(350/350-3)
SECOND QUESTION: f2=312(350/350+3)
THIRD QUESTION: SECOND QUESTION - FIRST QUESTION

Is that right?