146. A simple regular $(-4)$-regular graph with 6 vertices has how many edges of length 4? (1) $9$ (2) $10$ (3) $12$ (4) $15$
\textbf{146.} A simple regular $(-4)$-regular graph with 6 vertices has how many edges of length 4?
(1) $9$ \hfill (2) $10$ \hfill (3) $12$ \hfill (4) $15$
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