Calculate Period of Planet X with Kepler's Third Law

[meemosewa]

Using Kepler's Third Law, give the formula for the period TX of planet X whose orbital radius RX is twice that of earth, RE.

A. TX=(1 Year)x(RX/RE)^3
B. TX^2=(1 Year)x(RX/RE)^3
C. TX=(1 Year)x(RE/RX)^3
D. TX^2=(1 Year)x(RE/RX)^3

My book is not giving me a formula to use, so i a totally stuck... and ideas?

 

[Parlyne]

What does Kepler's third law say?

 

[meemosewa]

thats part of the problem, i don't know what it says

 

[dav2008]

Google:

http://www.google.com/search?source...GGL,GGGL:2005-09,GGGL:en&q=kepler's+third+law