Answer
(a) $617Hz$
(b) $583Hz$
Work Step by Step
(a) The frequency heard by the observer is given as
$f^{\prime}=(\frac{1}{1+\frac{u}{v}})f$
We plug in the known values to obtain:
$f^{\prime}=(\frac{1}{1+(18.5)(343)})(650)=617Hz$
(b) The frequency heard by the engineer is given as
$f^{\prime \prime}=(1-\frac{u}{v})f$
We plug in the known values to obtain:
$f^{\prime\prime}=(1-\frac{18.5}{343})(616.7)=583Hz$
