How many vertices does a decahedron have?

Answer 1

Unfortunately a hexahedron is an ambiguous term. It means a solid object with six plane faces. But that is not enough to uniquely identify shape:

it could be two triangular pyramids with their bases stuck together (a triangular dipyramid), which has 5 vertices (and 9 edges)

or

it could be a pentagonal pyramid, which has 6 vertices (and 10 edges)

or

it could be a parallelepiped (eg cube), which has 8 vertices (and 12 edges).

Answer 2

i say its 12

* * * * *

It depends on the configuration. Here are some:

A nonagon-based pyramid will have 18 edges and 10 vertices;

An octagon based prism will have 24 edges and 16 vertices;

A pentagon-based dipyramid will have 15 edges and 7 vertices.

There are others.

Answer 3

12

* * * * *

A 3D hexagon cannot exist.

Answer 4

6