http://en.wikipedia.org/wiki/Hexahedron
Generally, a hexahedron is any polyhedron with six faces, most commonly a cube. No hexahedron has a hexagon for any of its faces; most have squares or triangles.
Infinitely many - if you have an infinite supply of the materials from which they are made.
there is 7 hexagons in the design
They have 6
None.
how many vertices does 3 hexagons and 8 rectangles have all together
A hexagon is a plane (2-dimensional) figure whereas a hexahedron is a solid (3-dimensional) shape. A hexagon is bounded by six straight lines whereas a hexahedron is bounded by six polygons.
20 hexagons
Infinitely many - if you have an infinite supply of the materials from which they are made.
Steel companies make steel bars in hexagons
An infinite number, if you cut them small enough.
Infinitely many. You can make a very, very long chain of hexagons, for example.
4 hexagons; A hexagon has 6 sides, thus, if you have 4 hexagons, 4x6=24
there is 7 hexagons in the design
None. Though there can be ten if the hexagons are concave hexagons.
No. Not even all hexahedrons are cubes.
6
6