Question

find the value of x.

Explanation:

Step1: Identify vertical - angle relationship

Vertical angles are equal. So, $3x + 6=123$.

Step2: Solve for $x$

Subtract 6 from both sides: $3x=123 - 6$.
$3x = 117$.
Divide both sides by 3: $x=\frac{117}{3}$.
$x = 39$.

Answer:

$39$