I need help answering these questions

A woman is sitting at a bus stop when an ambulance with a siren walling at 405 Hz approaches at 29.5 m/s (about 66 mph). Assume the speed of sound to be 343 m/s. (a) What frequency (In Hz) does the woman hear? fa Hz (b) With what speed v (In m/s) would the ambulance have to travel in order for the woman to hear the siren at an apparent frequency of f = 426 Hz? V S m/s (c) What frequency (in Hz) would the woman hear If the siren moved away from her with the same speed you found In part (b)? fa = Hz