If 2 angles are formed on a line, then they make a supplementary / linear pair of angles, i.e, both the angles form 180°.
Here,
Angle A = 80°
Angle B = x°
So,
Angle A + Angle B = 180°
80° + x° = 180°
x° = 180° - 80°
x° = 100°
=》 Angle B = 100°
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Hope it helps ⚜
