Waves

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 the direction of wind which is blowing at 72 kmh^\(-\)1 speed. Frequency of siren is 720 Hz. The employee hears an apparent frequency of ____________ Hz.

(Assume speed of sound to be 340 ms^\(-\)1)