A "rectangular" is an adjective, not a noun and so there is no way of knowing what the shape is. It could be a rectangular 2-d shape, a rectangular pyramid, a rectangular prism and they would all have different answers.
A rectangular prism has 6 flat surfaces
It has 6 faces which are its flat surfaces.
8
6 flat surfaces - known as faces, 12 edges 8 vertices.
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.
A "rectangular" is an adjective, not a noun and so there is no way of knowing what the shape is. It could be a rectangular 2-d shape, a rectangular pyramid, a rectangular prism and they would all have different answers.
A rectangular prism has 6 flat surfaces
It has 6 faces which are its flat surfaces.
six
6
8
6 flat surfaces - known as faces, 12 edges 8 vertices.
cube There are a great many solid shapes that have only flat surfaces.
There are two definitions for 'cuboid', but they both describe a shape with six flat surfaces (or 'faces').
A rectangular prism is basically an elongated cube. Just like a cube, it has six sides.
There are six faces in a rectangular prism6 faces