Next question, question says, the siren emitting a sound of frequency 800 hertz, move away from an observer towards a cliff at a speed of 15 meter per second. Then the frequency of sound, that the observer hears in the eco reflected from the cliff is, and we have said that we can take velocity of sound here at 330. Again, the question is simple, direct formula will be applied, first you think situation here, so this is our situation, that this is the main reason for this, and this is the car, the velocity is coming from the car, and this is a cliff here, and this is your observer. This car has turned the sound here, it has turned on, the sound is here, and the pressure is passed by the observer. In that case, the question is, what will happen in case of F dash? If your original frequency is F, now, here the question is different, we have to apply some cases in two times the Doppler effect, it will not be in this case, because in those cases, we say that the driver of this case is the same, if the eco will come back, in that case, we have to apply Doppler effect in two times, but in this case, we will not apply Doppler effect in this case, it will work on its own. So here, our F dash will be, we know it, we will apply V of your speed of sound, plus V naught divided by V minus V s multiplied by F, this is your formula, here your observer speed is zero, so this portion will be zero to you, the rest of the data will be the final value, V is your 303, so this is 303, divided by 303 minus 15, multiplied by its frequency, 800 hertz, 800 dV, 800 hertz, but it will calculate its answer, so this will be 330 divided by 315, multiplied by 800, so when we calculate it, then our answer will be 338, so F dash will be equal to 838 hertz, so this will be our final answer, so based on this, we can say option number A, 838 would be the right answer.