To solve for \( x \) in the given problem, we can use the property of vertical angles, which states that vertical angles are equal. Since \( \angle 1 \) and \( \angle 3 \) are vertical angles, we have:
\[ m\angle 1 = m\angle 3 \]
Substituting in the values given in the problem:
\[ 3x - 25 = 104 \]
Now, we will solve for \( x \).
- Add \( 25 \) to both sides:
\[ 3x - 25 + 25 = 104 + 25 \]
This simplifies to:
\[ 3x = 129 \]
- Next, divide both sides by \( 3 \):
\[ x = \frac{129}{3} \]
Calculating the right-hand side gives:
\[ x = 43 \]
Thus, the value of \( x \) is \( \boxed{43} \).