Answer
Factor $6$ out of each column, or, factor $6$ out of each row.
Work Step by Step
$$
\left|\begin{array}{cccc}{6} & {0} & {0} & {0} \\ {0} & {6} & {0} & {0} \\ {0} & {0} & {6} & {0} \\ {0} & {0} & {0} & {6}\end{array}\right|=6^{4}\left|\begin{array}{cccc}{1} & {0} & {0} & {0} \\ {0} & {1} & {0} & {0} \\ {0} & {0} & {1} & {0} \\ {0} & {0} & {0} & {1}\end{array}\right|.
$$
Factor $6$ out of each column, or, factor $6$ out of each row.