\(\tan \theta=\frac{\sqrt{3}}{1}\)

\(0=60^{\circ}\)

If at any instant the line joining moving source and stationary observer makes an angle \(\theta\) with the direction of motion of source,

\(f^{\prime}=f\left(\frac{c}{c-v \cos \theta}\right)\)

Where \(c\) is speed of sound and \(v\) is speed of source

\(f^{\prime}=640\left(\frac{330}{330-20 \cos 60^{\circ}}\right)=640\left(\frac{330}{320}\right)\)

\(f=660\,Hz\)