Answer:
∠ DBC = 16°
Step-by-step explanation:
∠ ABD + ∠ DBC = ∠ ABC , substitute values
2x + 15 + x - 30 = 123 , that is
3x - 15 = 123 ( add 15 to both sides )
3x = 138 ( divide both sides by 3 )
x = 46
Thus
∠ DBC = x - 30 = 46 - 30 = 16°
