There is no such thing as a 3d triangle. A 3d shape which has only equilateral triangular faces can be a tetrahedron which has 4 faces or an icosahedron which has 20.
Only one; a triangle is a 2D shape, not a 3D shape. Usually only 3D (or more) shapes are considered to have 'faces'.
none because a triangle is not a 3D object
A pyramid.
A tetrahedron (4 faces) and an icosahedron (20).
Yes, and three rectangular faces.
1 Face (2D) 4 Faces (3D) 3 Sides 3 Points, and 2 Congruent sides.
A 3D shape with one base and three faces can only have triangular faces.
Sum the areas of all four faces.
Six faces
A di-pentagonal pyramid: which is two pentagonal pyramids with their pentagonal faces stuck together.
A tetrahedron (triangular pyramid).