Two spheres with different masses, \( m \) and \( M \), are separated by a distance \( d \) between their centers. If the gravitational field strength due to the sphere of mass \( M \) at the position of the center of the sphere with mass \( m \) is \( X \), what is the field strength due to the sphere of mass \( m \) at the position of the center of the sphere of mass \( M \)? Select TWO answers.