Well here, this is easy so i hope i help. You said this shape has 15 sides great. seeing that a prism is a 3D figure its gonna expand right? There's 15 sides . but don't forget about the sides faces of the prisms. There's 2 . Meaning all you have to do is count the sides and faces of the prism. Getting 17. Hope this helps.
Hmm. a rectangle?ok then, least number of rectangles needed-6. . . . . . . ( rectangle) so, 6 x 8=48(greatest multiple of 6 from between 21 and 49) 48 players are most, so 8 rectangles