\[\begin{array}{l}
b)\,\,\,Ta\,\,\,co:\,\,\angle ABC'\,\,va\,\,\,\angle ABC\,\,\,la\,\,\,2\,\,goc\,\,ke\,\,bu\\
\Rightarrow \angle ABC' + \angle ABC = {180^0}\\
\Rightarrow \angle ABC' = {180^0} - \angle ABC = {180^0} - {56^0} = {124^0}.\\
c)\,\,\,Vi\,\,\angle C'BA'\,\,va\,\,\angle ABC'\,\,la\,\,\,hai\,\,goc\,\,ke\,\,bu\\
\Rightarrow \angle C'BA'\,\, + \,\,\angle ABC' = {180^0}\\
\Rightarrow \angle C'BA' = {180^0} - \angle ABC' = {180^0} - {124^0} = {56^0}.
\end{array}\]