Math 圓的性質 急！！?

Set angle a = ∠BCE = ∠BCD = arc(BD)/2

for ΔACE: 2a + 15° + 63° + 90° = 180° ==>> a = 6°

for ΔBCE: x + 6° + 63° + 90° = 180° ==>> x = 21° = (B)

Answer = (B)