Supplementary angles are two angles whose measures add up to 180°. Since you have m∠ABC = 105° and m∠CBE = (3x + 24)°, you can set up the following equation to solve for \( x \):
\[ m ∠ ABC + m ∠ CBE = 180° \]
Substituting the given expressions into the equation:
\[ 105° + (3x + 24)° = 180° \]
This is the equation that is set up correctly to solve for \( x \).