Remember that vertical angles are pairs of opposite angles made by two intersecting lines. Since vertical angles are congruent, we can equate the measures of angle 4 and angle 8 and solve for [tex]x[/tex]:
[tex]3x=x+40[/tex]
[tex]2x=40[/tex]
[tex]x= \frac{40}{2} [/tex]
[tex]x=20[/tex]
We can conclude that the measure of angle of is 20°
