So I need some help with this problem:

Newton's Law of Gravitation states that the magnitudeFof force exerted by a body of massmon a body of mass M is F(r)=(GmM)/r^2, where G is the gravitational constant and r is the distance between the center of the bodies. Suppose that one of the bodies is the earth and the other is a 1000-kg satellite. The earth's mass is approximately 5.98(10^24) kg concentrated at the center and its radius is approximately 6.37(10^6)m. G=6.67(10^-11) N * m^2/kg^2

a. Determine how fast the force between the earth and satellite changes when the satellite has launched vertically to a height of 1000 km.

b. Explain the physical meaning of the minus sign for the rate of force with respect to the distance between the bodies.

c. The determination of work required, when a force and change in distance is given, is analogous to determining the displacement when the velocity and change in time is given or the change in charge when the current and the change in time is given. Compute the work required to launch the satellite vertically to a height of 1000 km.

I really need some help trying to figure out what I need to do in order to proceed with this problem. Don't want the answers just help solving it

Thanks in advance