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 times **as long.
According to Kepler's Third Law, if planet A is four times farther from the Sun than planet C, then the period of A's orbit will be 8 times longer than that of C. This is because the orbital period is proportional to the cube of the distance from the Sun. Thus, the answer is that the period of the orbit will be 8 times as long.
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