An assignment of probabilities for outcomes of the sample space \( S = \{1, 2, 3, 4, 5, 6\} \) is as follows:
\[
\begin{array}{c|c c c c c c}
1 & 2 & 3 & 4 & 5 & 6 \\
\hline
k & 3k & 5k & 7k & 9k & 11k
\end{array}
\]
If this assignment is valid, then the value of \( k \) is: