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.