Answer:
80°
Explanation:
You want the sum of angles 1 and 2 in the attached figure where line m ║ line n.
Vertical angles
Vertical angles are congruent. This means angle 1 is 60°, and the unnumbered angle in triangle ABC at vertex A is 20°.
Alternate interior angles
Where a transversal crosses parallel lines, alternate interior angles are congruent. This means angle 2 is congruent with the unnumbered interior angle at A, which we know is 20°.
Angle 1 is 60° and angle 2 is 20°. Their sum is ...
∠1 +∠2 = 60° +20° = 80°
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