The diagram show the net of a regular octohedron.

In a Magic Octahedron, the four numbers on the faces that meet at a vertex add up to make the same total for every vertex. If the letters $F, G, H, J$ and $K$ are replaced with the numbers $2, 4, 6, 7$ and $8$, in some order, to make a Magic Octohedron, what is the value of $G + J$?

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This problem is taken from the UKMT Mathematical Challenges.

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