## Elementary Geometry for College Students (6th Edition)

m$\angle$ABD=56$^{\circ}$
Given: support system of a bridge which has AC=6ft m$\angle$ABC=28$^{\circ}$ m$\angle$CBD=m$\angle$ABC=28$^{\circ}$ because they are corresponding angles of congruent triangles therefore, m$\angle$ABD=m$\angle$ABC+m$\angle$CBD m$\angle$ABD=28$^{\circ}$+28$^{\circ}$ m$\angle$ABD=56$^{\circ}$