Final answer:
If Planet X has a moon similar to Earth's moon, it would follow an elliptical orbit around the planet. If the planet no longer exists, the moon would continue to move in a straight line until acted upon by another force.
Step-by-step explanation:
The moon's orbit around a planet is determined by the gravitational force between the two celestial bodies. If Planet X has a moon similar to Earth's moon, it would follow an elliptical path around the planet. This path would be determined by the balance between the moon's gravitational attraction towards the planet and its inertia, causing it to orbit in a nearly circular path.
If the planet were to be destroyed and no longer exist, the moon would continue to move in a straight line at a constant speed until acted upon by another force. This is known as Newton's first law of motion, which states that an object in motion will stay in motion with the same speed and direction unless acted upon by an external force.
Learn more about Moon's orbit around a planet