Two angles are supplementary if their measures add up to 180 degrees. Given the measures of the angles as \( \angle ABC = 135^\circ \) and \( \angle CBD = 9x^\circ \), you can set up the following equation:
\[ 135 + 9x = 180 \]
Now, you can rearrange this equation to solve for \( x \).
From the provided responses, the correct equation is:
9x + 135 = 180