If planet A is four times as far from the sun as planet C, then the period of its orbit will be__ times as long

Within the system of the same star, the period of a planet's orbit is

proportional to the 3/2 power of its distance from the central body.

(Kepler's empirical third law of planetary motion, promoted to being

etched in stone by Newton's gravitation.)

(4) ^ 3/2 = 8 timesas long.