Kepler's third law says that the size of a planet's orbit, as measured by its semimajor axis, is related to the period of the orbit. If you measure the size of the orbit in astronomical units and the period in years, then the relation is simply:
(period)² = (semimajor axis)³
If you were to discover a new planet with a semimajor axis of 4 astronomical units, what would its period be?
    A ) 4 years
    B) 8 years
    C) 16 years
    D) 64 years

When called for, hold up the letter of your choice.