A triangular based prism has 6 vertices and 9 edges.
9 edges
Well you have an octagon on each end of the prism, and octagons have 8 sides, so 8 x 2 is 16, and then you have edges connecting the corners of the octagons at the end. There are 8 corners in an octagon, so that's 8 more edges. 16 + 8 = 24 total edges. An n-gonal prism has 3n edges.
6 edges 4 vertexes
If the prism is based on regular decagons and it is a right prism, all 12 faces.
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.
A triangular based prism has 6 vertices and 9 edges.
9 edges
Well you have an octagon on each end of the prism, and octagons have 8 sides, so 8 x 2 is 16, and then you have edges connecting the corners of the octagons at the end. There are 8 corners in an octagon, so that's 8 more edges. 16 + 8 = 24 total edges. An n-gonal prism has 3n edges.
7
12
15
9
9
An octagon has 8 edges
An octagon has 8 sides or edges
there are 12 (twelve) edges.