The variable period of a moon of Jupiter, which is the basis of measurement of the speed of light in Roemer's method (whoever heis), is regarded as the Doppler affect. The period of the orbital motion of one of Jupiter's moons is approximately42.5hours; the speed of light is 2.99e8 m/s. The orbital speed of the Earth about the Sun is 2.98e4 m/s. What is the maximum change in the period (in seconds) of this moons observed from Earth? (hint: T = 1/f)

I've done Doppler problems with two moving objects
but I cant come up with an answer that makes sense.
How do i use frequency to solve this? (thanks the other"kp")