K_8 has 28 edges k_4 + k_4 has 6+6 12 edges

let the graph k_8 have vertices x1,x2,x3,x4,x5,x6,x7,x8

consider a
First graph k_4 with x1,x2,x3,x4 and the edges from x1,x2,x3 to the vertices x5,x6 and x4 to x7,x8

second graph k_4 with x5,x6,x7,x8 and the edges x4 to the vertices x5,x6 and the edges x1,x2,x3 to x7,x8

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