To find the equation to solve for \( x \) given that two angles are supplementary, you can use the fact that the sum of supplementary angles equals 180°. In this case, you have:
- \( m∠ABC = 135° \)
- \( m∠CBD = 9x° \)
Since these two angles are supplementary, the equation to express this relationship is:
\[ 9x° + 135° = 180° \]
So, the correct response is:
9x° + 135° = 180°