In the equation \( y = \frac{x}{9} \), we can rewrite it in the form \( y = kx \), where \( k \) is the constant of proportionality.
In this case, \( k \) can be identified as:
\[ k = \frac{1}{9} \]
Thus, the constant of proportionality is \( \frac{1}{9} \).
The correct answer is:
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