Two spheres a and b of mass 6.5 kg and 8.3 kg, respectively, are separated by a distance of 0.56 m. (a) calculate the magnitude, in n, of the gravitational force a exerts on b and b exerts on a. force a exerts on b n force b exerts on a n (b) if the force between the spheres is now 3.50 10-9 n, how far apart are their centers, in meters