Answer:
21°
Step-by-step explanation:
The measure of arc AC is twice the measure of the inscribed angle ABC, thus
3x + 9 = 2(3x - 1.5) ← distribute
3x + 9 = 6x - 3 ( subtract 6x from both sides )
- 3x + 9 = - 3 ( subtract 9 from both sides )
- 3x = - 12 ( divide both sides by - 3 )
x = 4
Thus
arc AC = 3x + 9 = 3(4) + 9 = 12 + 9 = 21°
