AU is a unit of distance. AU is the abbreviation for the astronomical unit. The astronomical unit is the average distance between the Earth and the Sun. The equivalent of 1 Astronomical unit in kilometres is 1.5 x 10⁸ Km. Now it is given that the distance of the Saturn from the Sun is 1.5 billion kilometres i.e., 1.5 x 10⁹ Km. This can be written as 1.5 x 10⁸ x 10 Km. This distance is equivalent to 10 AU. Therefore, Saturn is 10 AU far from the Sun.