What are arithmagons?
A arithmagon is a polygon (here a triangle) with the operands at its vertices and the sums of the vertices written on the edges.
There are kind of puzzles.
2. The most difficult. The sums on the edges are given. You have to find the operands at its vertices. You can do this by trial and error or find a more mathematical/algebra approach.
3. Not to difficult. This is a mixed of the first two puzzles. 2 sums on the edges are given and one operand at the vertex.