Multiple choice: Earth is at a distance of 1 AU from the Sun and has an orbital period of 1 year. Suppose a hypothetical planet "Xander" orbits the Sun with an orbital period of 8 years. What is Planet Xander's average distance from the Sun?
(a) 4 AU.
(b) 2 AU.
(c) 64 AU.
(d) 8 AU.
(e) 83/2 AU.