Vertical angles are congruent, which means their measures are equal. Given that \( m∠2 = 135° \) and \( m∠4 = (4x + 15)° \), we can set them equal to each other:
\[ 135 = 4x + 15 \]
Now, we will solve for \( x \):
- Subtract 15 from both sides:
\[ 135 - 15 = 4x \]
\[ 120 = 4x \]
- Divide by 4:
\[ x = \frac{120}{4} \]
\[ x = 30 \]
Thus, the value of \( x \) is \( 30 \).