Answer:
The measure of angle C is 80 degree.
Explanation:
Given information: In ΔABC, ∠A = 40° and ∠B = 60°.
Draw the auxiliary line BD parallel to the line segment AC.
If a transversal line intersects the pair of parallel line, then the alternate interior angles are same.
The angle 1 and 2 are alternate interior angles of angle A and B respectively. Therefore angle 1 is equal to angle A and angle 2 is equal to angle C.
Angle 1,2 and B are supplementary angles because they lie on a straight line, therefore their sum is 180 degree.





The angle sum property is another way to solve this problem.
According to the angle sum property, the sum of interior angles of a triangle is 180 degree.
Therefore the measure of angle C is 80 degree.