the branch of mechanics concerned with the motion of objects without reference to the forces which cause the motion.
Answer:
Planet Y
Rx = 1.587 Ry
Explanation:
Tx = 290 days
Ty = 145 days
Let the semi major axis of planet X is Rx and of plant Y is Ry.
According to the Kepler's third law of planetary motion




Rx = 1.587 Ry
So, planet Y is closest to star.