[relativistic]

the satellite is orbiting under equilbrium of 2 forces , the centrepital force and centrifugal force which are equal so

mass * 8.21=mass *v^2 / distance from centre of earth

algebric solving of this equation
v^2=8.21 * (600 +6400) ok
we get the velocity.

then calculate the circumference of its orpit by law
circ.= pi *2*r

circ.= 2*pi*7000

divde this distance by the velocity you get from the first answer and you will get time.

sorry i can`t understand the second problem.