physics help?

Rearranging the general formula yields:

T = 2𝞹 √(r³/(GM₁)) as the mass of the satellite cancels out. G is universal gravity constant.

sub in your values and then change units to days.

I won't do your homework for you but maybe this will help.  

Newton's Law is F=Gmm/R^2  You can get the acceleration by dividing the mass of the Satellite.

The acceleration is a=v^2/R since it has to balance gravity for an orbit.....

You can solve for v. 

The circumference of the orbit is C=2 pi R

At a velocity of v you can figure out how long to go around.

You probably now have the time in seconds for an orbit.  depending on the units you had for G (be cautious about the units, the units in the problem are meters and kilograms so G in mks or cgs will mean you need to get the units of either R or m in that system you chose)

An earth year is about pi x 10^7 seconds but you can work that out from 365.23 days per year.

For a circular orbit of radius r,

T = 2pi sqrt(r^3 / (GM))