Answer:
[tex]10x = 18 + x \\ \\ 10x - x = 18 \\ \\ 9x = 18 \\ \\ \frac{9x}{9} = \frac{18}{9} \\ \\ x = 2 \\ \\ 10x = 10(2) = 20 \\ \\ 18 + x = 18 + 2 = 20[/tex]
Vertical angles are congruent.
