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I get a different answer than welshbyte. The "long" diagonals are indeed 10cm long, but for the shorter ones I get 5*sqrt(3) or ~8.66.
I get this answer from the Law on Sines: x/sin(120) = 5/sin(30).
The total length would be 3*10 + 6*(5*sqrt(3)), or ~81.96.
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