\(\displaystyle{\underset{{{f}{i}{g}{u}{r}{e}}}{{{A}}}}={\underset{{\boxempty}}{{{A}}}}+{\underset{{\triangle}}{{{A}}}}\)

\(\displaystyle{\underset{{\boxempty}}{{{A}}}}={\underset{{\boxempty}}{{{l}}}}^{{2}}\)

\(\displaystyle{\underset{{\boxempty}}{{{l}}}}=\frac{{{\underset{{{f}{i}{g}{u}{r}{e}}}{{{P}}}}-{2}\times{\underset{{\triangle}}{{{l}}}}}}{{3}}\)

\(\displaystyle=\frac{{{56}-{20}}}{{3}}\)

\(\displaystyle=\frac{{36}}{{3}}\)

=12cm

\(\displaystyle{\underset{{\triangle}}{{{A}}}}=\frac{{1}}{{2}}\times{b}{h}\)

\(\displaystyle=\frac{{1}}{{2}}\times{8}\times{12}\)

\(\displaystyle={48}{c}{m}^{{2}}\)

\(\displaystyle{\underset{{{f}{i}{g}{u}{r}{e}}}{{{A}}}}={12}^{{2}}+{48}\)

=144+48

\(\displaystyle={192}{c}{m}^{{2}}\)

\(\displaystyle{\underset{{\boxempty}}{{{A}}}}={\underset{{\boxempty}}{{{l}}}}^{{2}}\)

\(\displaystyle{\underset{{\boxempty}}{{{l}}}}=\frac{{{\underset{{{f}{i}{g}{u}{r}{e}}}{{{P}}}}-{2}\times{\underset{{\triangle}}{{{l}}}}}}{{3}}\)

\(\displaystyle=\frac{{{56}-{20}}}{{3}}\)

\(\displaystyle=\frac{{36}}{{3}}\)

=12cm

\(\displaystyle{\underset{{\triangle}}{{{A}}}}=\frac{{1}}{{2}}\times{b}{h}\)

\(\displaystyle=\frac{{1}}{{2}}\times{8}\times{12}\)

\(\displaystyle={48}{c}{m}^{{2}}\)

\(\displaystyle{\underset{{{f}{i}{g}{u}{r}{e}}}{{{A}}}}={12}^{{2}}+{48}\)

=144+48

\(\displaystyle={192}{c}{m}^{{2}}\)