Waves Part 1

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 72kmh−1 in the direction of wind which is blowing at 72kmh−1 speed. Frequency of siren is 720‌Hz. The employee hears an apparent frequency of ______Hz.
(Assume speed of sound to be 340ms−1 )