An employee of a factory moving away from his workplace by a car listens to the siren of the factory. He drives the car at the speed of 72 kmh^-1 in…

An employee of a factory moving away from his workplace by a car listens to the siren of the factory. He drives the car at the speed of $\displaystyle 72 \mathrm{kmh}^{-1}$ in the direction of wind which is blowing at $\displaystyle 72 \mathrm{kmh}^{-1}$ speed. Frequency of siren is $\displaystyle 720$ Hz . The employee hears an apparent frequency of \_\_\_\_ Hz. (Assume speed of sound to be $\displaystyle 340 \mathrm{~ms}^{-1}$ )