To find the equation to solve for \( x \), we need to remember that supplementary angles add up to \( 180^\circ \).
Given:
- \( m∠ABC = 135^\circ \)
- \( m∠CBD = 9x^\circ \)
We can express the relationship of the two angles as: \[ m∠ABC + m∠CBD = 180^\circ \]
Substituting the values we have: \[ 135^\circ + 9x^\circ = 180^\circ \]
This simplifies to the equation: \[ 9x^\circ + 135^\circ = 180^\circ \]
Therefore, the correct equation to solve for \( x \) is: 9x° + 135° = 180°