1. given
2. measure angle 1 plus measure angle 2 equals 90 degrees
3. B D bisects angle A D C
4. definition of angle bisector
5. definition of congruence
6. measure angle 1 is equal to measure angle 3
7. angle 1 is congruent to angle 3
7. definition of congruence
hope that helps
Answer:
15 degrees less --> substract 15 degrees.
78.6 - 15 = 63.6 degrees