A tetrahedron is a solid figure with 6 edges.
There's no such thing as solid edges.
A tetrahedron is a triangular pyramid, with 4 vertices, 6 edges and 4 triangular faces. In a regular tetrahedron (the first Platonic solid) all triangles are equilateral.
6
It is a hexahedron
There is no solid figure with only four edges. The smallest solid figure is the tetrahedron, made up of four triangular faces, but it has six edges.
You have to count the lines on a solid figure
A triangular prism
cube
A triangular pyramid has 4 faces and has 6 edges
A tetrahedron.
A basic pyramid with three sides?
No normal polyhedron.
square
A triangular pyramid.