Show that if the earth attracts two bodies, A and B placed at the same distance from the centre of the earth with the same force, then their masses are equal

let them be separated from earth at a distance of r each having masses as Ma and Mb

and masss of earth be Me

thus force between A and earth: Fea = GMeMa/r²

and force between B and earth: Feb = GMeMb/r²

thus Fea = Feb

hence Ma = Mb