Answer:
m∠C = 100°
Explanation:
In the congruent triangles, ∠E corresponds to ∠B (both are listed 2nd in the designators ABC and DEF). Those corresponding angles have the same measure.
Since the sum of angles of a triangle is 180°, we have ...
m∠A +m∠B +m∠C = 180°
55° + 25° + m∠C = 180°
m∠C = 100° . . . . . . . . subtract 80°