Explanation:
Given Angle CBD = 30,
Angle ABC + Angle CBD = 180 (Sum of Angles on the same straight line)
Angle ABC + 30 = 180
Angle ABC = 180 - 30 = 150
Since Angle AB =~ BC,
Angle A = Angle C
Let angle A and C be x.
Angle A + Angle C + Angle ABC = 180 (Sum of Angles in a triangle)
Therefore Angle A = 15 degrees