Since ∠2 and ∠4 are vertical angles, their measures are equal. Therefore, we can set up the equation:
\[ m∠2 = m∠4 \]
Substituting the given measures:
\[ 135° = (4x + 15)° \]
Now we can solve for \( x \):
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Subtract 15 from both sides: \[ 135 - 15 = 4x \] \[ 120 = 4x \]
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Divide both sides by 4: \[ x = \frac{120}{4} \] \[ x = 30 \]
So, the value of \( x \) is 30.