Assuming a regular decagon is the base of the prism, it would be 10 faces.
With an irregular decagon, it is possible that two (or more) of the edges of the decagons are perpendicular, so all 12 faces could have perpendicular edges.
A decagonal based pyramid will have 11 faces, 11 vertices and 20 edges
If the prism is based on regular decagons and it is a right prism, all 12 faces.
Edges = 30 Faces = 12 Vertices = 20
12 faces 20 vertices 30 edges
20
20 edges, 11 vertices (corners) and 11 faces.
An heptagonal based prism, also known as a heptagonal prism, has two faces that are perpendicular to each other. These faces are the bases of the prism, which are heptagons in this case. The perpendicular edges are the edges that connect the vertices of the bases at right angles, resulting in a total of 14 perpendicular edges in a heptagonal prism.
Vertices: 20 Edges: 30 Faces: 12
19 * * * * * Actually it is 30 edges. Ten around each of the decagonal faces, and ten more connecting the corresponding vertices of the two decagons.
12 faces * * * * * Correct as far as it goes, but incomplete. 20 vertices 30 edges
Not sure what a decagonal is. Since the question refers to faces, edges and vertices, it may be assumed that the object in question is 3-dimensional. A decagon certainly is not, so decagonal cannot be a mistaken name for a decagon.
A pyramid has one more corner and faces than the number of sides in its base; thus a decagonal pyramid has 10 + 1 = 11 faces and corners. A pyramid has twice as many edges as sides in its base; thus a decagonal pyramid has 2 X 10 = 20 edges.