Need help figuring our periods of planets

[Talontuner]

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?

 

[Kurdt]

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.

 

[Talontuner]

Thank you!