Angles
Though not specified, I'll assume lines s, t, and u are parallel
Note angle 4 is opposed to angle 2 by the vertex
Thus both angles are congruent
Angle 2 measures 80°
Since s and t are parallel, the angles they form with line m are congruent
Thus, angle 6 is congruent with angle 2
Angle 6 measures 80°
Correct choice. The second option: 80