There are four triangles in the pyramid.
The base triangle that supports the other three counts as THREE straws, one per each of the three sides.
But the remaining three triangles also use the base triangle for one of their three sides. That means there are only two additional straws for each of the three remaining triangles. So there are SIX straws total in the three triangles supported by the base one.
That's a sum total of NINE (9) unique straws in the pyramid...3 in the base and 2 each in the three supported triangles. ANS.
To build the skeleton of a triangle-based prism, you would need 9 straws: 3 for each edge of the triangle base (totaling 9 straws) and 6 additional straws to connect the vertices of the triangle to form the prism.
six, you need six
9.
2 faces
6,6
8 straws.
18 straws.
10
15
24
3
9