33. please help thank you

33. On a standard day the speed of sound is 345 meters per second. A whistle whose frequency is 725 Hz is moving toward an observer at a speed of 25.2 meters per second. What is the wavelength of the sound at the observer? 12) 0.367 m (b) 0.441 m (c) 0.511 m (d) 0.623 m