Angle Sum Theorem Acellus
20 120 y = ?

We know
Sum of two interior angles=exterior angle
[tex]\\ \sf\longmapsto 20°+120°=<y[/tex]
[tex]\\ \sf\longmapsto <y=20°+120°[/tex]
[tex]\\ \sf\longmapsto <y=140°[/tex]
Hope it helps