Треугольник равнобедренный (AB = BC), поэтому \(\angle \,A = \angle \,C.\)
\(\angle \,ABC = {180^ \circ } — \angle \,CBD = {180^ \circ } — {138^ \circ } = {42^ \circ }.\)
\(\angle \,A + \angle \,C + \angle \,ABC = {180^ \circ }\,\,\,\,\,\,\, \Leftrightarrow \,\,\,\,\,\,\,\,2\angle \,C = {180^ \circ } — {42^ \circ }\,\,\,\,\,\,\, \Leftrightarrow \)
\( \Leftrightarrow \,\,\,\,\,\,\,2\angle \,C = {138^ \circ }\,\,\,\,\,\,\, \Leftrightarrow \,\,\,\,\,\,\,\,\angle \,C = {69^ \circ }.\)
Ответ: 69.