Triangles BAD and BCD are congruent by the HL theorem. That is, they have identical length hypotenuses (BD) and one leg is also identical in length to that in the other triangle. (AD ≅ CD)
Since the triangles are congruent, corresponding angles are equal, so ∠CBD = ∠ABD = 28°. The angle you are interested in is the sum of these two angles,
... ∠ABC = 28°+28° = 56°
