Calculation of a planet's mass via wavelengths

[Poppinkrey]

I got to find an answer or a push to the right tracks on this question.

Suppose a spacecraft is in a circular orbit about a distant planet. the spacecraft emits a continuous radio signal with a wavelength of 6m. The signal's wavelength varies between 5.99969m and 6.00031m; the period of variation (full period of wavelength) is 5 hours. What is the mass of the planet? Assume that you are located in plane of the spacecraft 's orbit and knowing that circumference is 2piea (a = radius) and that speed = distance / time.

Thanks in advance!

 

[Poppinkrey]

I believe this requires kepler's 3rd law (where the common focus is in the distant planet).

 

[DrStupid]

I believe this requires kepler's 3rd law

That's a good idea. You can also use Newton's law of gravitation. Now you have to include the given frequencies. Do you know a relationship between velocity and frequency shift?