Since this is only worth one credit, I am going to assume you know the derivation of the following equation from Kepler's laws: GMm/(R + r)^2 = mw^2r w is omega for my type font.
For M>>>>m r is >>>R and this equation simplifies to a cubic in r and w is the period divided by 2 x pi , ...
This solution identifies and explains required calculations, however, the student must complete the work on their own. A website for reference is included. 216 words.