Given:
m∠A = (3x - 9)
m∠B = (x + 3)
A and B are vertical angles.
Vertical angles are always congruent.
Thus,
m∠A = m∠B
3x - 9 = x + 3
Let's solve for x.
Add 9 to both sides:
3x - 9 + 9 = x + 3 + 9
3x = x + 12
Subtract x from both sides:
3x - x = x - x + 12
2x = 12
Divide both sides by 2:
[tex]\begin{gathered} \frac{2x}{2}=\frac{12}{2} \\ \\ x\text{ = 6} \end{gathered}[/tex]ANSWER:
x = 6
