Answer:
AB = 72°
Step-by-step explanation:
The inscribed angle ADC is half the measure of its intercepted arc, thus
56° = [tex]\frac{1}{2}[/tex] ( m ABC ) ← multiply both sides by 2
112° = ABC
ABC = AB + BC = AB + 40, so
AB + 40 = 112 ( subtract 40 from both sides )
