Answer:
The answer is 8 sides.
Explanation:
A plane intersects a prism parallel to the base of the prism. The cross section is a polygon with eight sides. The base of the prism has also 8 sides.
The cross-section of a plane parallel to the base is the same shape as the base. The cross section is also an eight sided polygon, so, the base of the prism has 8 sides.