physics mass question, please help :)

Question

We observe a moon going around a planet. The moon orbits with a period of 7.3 days and with an orbital radius of of 3.5 x 107 meters. Find the mass of the planet. Give your answer ...
in terms of kilograms, to a precision of 3 significant figures in scientific notation. Use a format like #.##e## in your answer.
For instance, if you want 4.27 x 1014 kg type in "4.27e14".

Answer 1

try:

GM/R=v², where v=(2*pi*R/T)