When two lines are cut by a transversal, the pair of angles formed interior of the two lines and on the opposite of the transversal is called Alternate Interior Angles.
If two parallel lines are cut by a transversal, the alternate interior angles are congruent
In the figure shown, l is the transversal that cut the pair of lines. Angles a and d and angles b and c are alternate interior angles.
D. Insufficient information
Correct Answer: C
Step 1: 120o + n = 180o [Straight angle.]
Step 2: n = 60o [Solve for n.]
Step 3: n = 60o implies m = 60o, because m and n are alternate interior angles and so they are congruent.