m<ABD = 52 Given
BC bisects <ABD Given
m<ABC = m<CBD Definition of angle bisector.
m<ABC +m<CBD = m<ABD Angle addition postulate.
m<ABC +m<CBD = 52 Substitution
m<ABC + m<ABC= 52 Substitution
2m<ABC = 52 Combining like angles
m<ABC = 26 Division property of equality.