JEE Advanced Model Paper 9 with solutions for online practice

Two sound sources are moving away from a stationary observer in oppositedirections with velocity V1 and V2 (V1 > V2) . The frequency of both the series is900Hz. V1 and V2 are both quite less than speed of sound, V = 300 m/ sec . Find thevalue of (V1−V2) , in m/sec, so that beat frequency observed by observer is 6 Hz.