A rectangular prism has 6 flat surfaces
six
6
6
It has 6 faces which are its flat surfaces.
8
A rectangular prism is basically an elongated cube. Just like a cube, it has six sides.
A prism with an n-sided base will have 2n vertices, n + 2 faces, and 3n edges.
six (like a cube which is a special rectangular prism, one with all sides the same length)
The question is ambiguous since a rectangular pyramid and a rectangular prism will have different numbers of flat surfaces. There is no indication in the question which shape is intended.
5
Given the surface area of a rectangular prism, there are infinitely many rectangular prisms possible.