6 i think
Just one, although the orientation of the prism might vary.
Ignoring rotations, there are 3 distinct solutions.
The answer depends on the number. Note that the question does not require the solids to be in the form of cubiods (rectangular prisms).
You can have the 18 as prisms, OR.. they can be cut up into an infinite number of different prisms, as many as your tools for cutting it can make.