A 3D shape with all straight edges and flat faces is a polyhedron. Other 3D shapes with least one curved surface are not polyhedra. A 3D shape with regular polygonal faces, meeting at equal angles ...

12 + 84 = 96. The total surface area of the prism is 96 cm². Image caption, The rectangular faces can be combined to form one rectangle. One edge of the rectangle is the perimeter of the triangle.