angle1 + angle2 = 180
[tex]4x + 20 + x + 20 = 180[/tex]
[tex]5x + 40 = 180[/tex]
[tex]5x = 180 - 40[/tex]
[tex]5x = 140[/tex]
[tex]x = \frac{140}{5} [/tex]
[tex]x = 28[/tex]
