Extrasolar Planets. In the not-too-distant future, it should be possible to detect the presence of planets moving

Question:

Extrasolar Planets. In the not-too-distant future, it should be possible to detect the presence of planets moving around other stars by measuring the Doppler shift in the infrared light they emit. H a planet is going around its star at 50.00 km/s while emitting
Infrared light of frequency 3330 x 1014 Hz, what frequency light will be received from this planet when it is moving directly away from us? (Note: Infrared light is light having wavelengths longer than those of visible light.)