Answer:
[tex] \tt{✧ \: S \: O \: L \: U \: T \: I \: O \: N : }[/tex]
[tex] \large{ \tt{✿ \: 3x = x + 80 \degree}}[/tex] [ Exterior angle is equal to the sum of two non - adjacent interior angles ]
[tex] \longrightarrow \: \tt{3x - x = 80 \degree}[/tex]
[tex] \longrightarrow \tt{2x = 80 \degree}[/tex]
[tex] \longrightarrow \tt{x = \frac{80 \degree}{2} }[/tex]
[tex] \longrightarrow{ \boxed{ \tt{x = 40 \degree}}}[/tex]
Hope this helps! ( ╹▽╹ )