The supplement of an angle is basically 180° minus that angle. In other words, two supplementary angles together add up to 180°.
If you let [tex]x[/tex] be the angle, then [tex]x[/tex] plus an angle eight times its measure is equal to 180°. Thus, [tex]x + 8x = 180[/tex], or [tex]9x = 180[/tex]. Therefore, [tex]x[/tex] = 20°.
