# how do i work this problem?

**Question description**

The Doppler effect (named after Christian Doppler) is the change in the pitch
(frequency) of the sound from a source *(s)* as heard by an observer *(o)* when one or both are in
motion. If we assume both the source and the observer are moving in the same direction, the
relationship is

f^1 = f a (v-vo) divided by (v-vs)

where *f ‘* = perceived pitch by the observer
*f a *= actual pitch of the source
*v* =speed of sound in air (assume 772.4 mph)
*vo* =speed of the observer
*vs* =speed of the source. Suppose you are traveling down the road at 45 mph and you hear an ambulance (with siren) coming
toward you from the rear. The actual pitch of the siren is 600 hertz (Hz).

(a) Write a function* f ′(vs)* that describes this scenario.

(b) If *f ′* = 620 Hz, find the speed of the ambulance.

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