A tridekahedron is a 3D 30 sided shape.
There is not a definite name for a 3D figure with 18 sides.It is possible that it is something else - but the information to test this is not provided.
Dodecahedron
A dodecahedron.
pentagonal pyramid
A hexahedron is the name for a 6 sided 3D shape.
the name of a 20 sided 3d shape is called a icosahedron
2D is a decagon. 3D is a decahydron.
HEXADECAHEDRON is the correct name for a 16 sided 3D object
Strictly speaking, any 3d figure with anything besides 6 sides cannot consist of rectangles. However, the name for an 8-sided figure is "octahedron".
no
There is no name for a five sided regular polygon. A five sided polyhedron is called a pentahedron.