This Application Problem is a part of the Lesson 19, Unit 4, Grade 5. Angle A of a triangle is the size of angle C. Angle B is the size of angle C. If angle C measures 80 degrees, what are the measures of angle A and angle B? Because today's fluency activity asks students to recall the content of Lesson 18, this Application Problem asks students to recall previous learning to find a fraction of a set.