Frequency of source, $v_{0}=100 \mathrm{Hz}$
Velocity of source, $v_{s}=19.4 \mathrm{ms}^{-1}$
Velocity of sound in air, $v=330 \mathrm{ms}^{-1}$
As the velocity of source along the source observer line is $v_{s} \cos 60^{\circ}$ and the observer is at rest, so the apparent frequency observed by the observer is
${v=v_{0}\left(\frac{v}{v-v_{s} \cos 60^{\circ}}\right)}$
${=(100 \mathrm{Hz})\left(\frac{330 \mathrm{ms}^{-1}}{330 \mathrm{ms}^{-1}-\left(19.4 \mathrm{ms}^{-1}\right)\left(\frac{1}{2}\right)}\right)}$
${=(100 \mathrm{Hz})\left(\frac{330 \mathrm{ms}^{-1}}{330 \mathrm{ms}^{-1}-9.7 \mathrm{ms}^{-1}}\right)}$
${=(100 \mathrm{Hz})\left(\frac{330 \mathrm{ms}^{-1}}{320.3 \mathrm{ms}^{-1}}\right)=103 \mathrm{Hz}}$
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Where $A$ and $K$ are positive constants
