Need help figuring our periods of planets

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To determine the orbital period of a planet located 3 A.U. from a star three times the mass of the Sun, Kepler's Third Law, revised by Newton, is applied using the formula P^2 = 4π^2/G(m1+m2) * R^3. In this case, m1 can be replaced with the mass of the star (3 times the Sun's mass) and m2 can be ignored since the planet's mass is negligible compared to the star's mass. The radius R is given as 3 A.U. The constants 4π^2 and G are used in the calculation to find the period P. Understanding how to manipulate this equation is crucial for solving the problem effectively.
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Homework Statement


OK here's the question: What is the period of a planet orbiting 3 A.U. from a star 3 times as massive as the sun? And my teacher says to use keppler's 3rd law revised by Newton but I am completely confused by the equation and how to use it on this problem.


Homework Equations


P^2= 4*pi^2/G(m1+m2) * R^3 is the equation


The Attempt at a Solution


I have no idea where to even begin... please help. Suggestions?
 
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The 4 pi squared and G are just constants. In this question you can replace m1 and m2 by just the mass of the sun, and r is the radius of the orbit which is given as 3AU.
 
Thank you!
 
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