\[a = 40\ см,\ \ b = 26\ см,\ \]
\[\ c = 52\ см:\]
\[S = 2 \cdot (ab + bc + ac) =\]
\[= 2 \cdot (40 \cdot 26 + 26 \cdot 52 + 40 \cdot 52) =\]
\[= 2 \cdot (1040 + 1352 + 2080) =\]
\[= 2 \cdot 4472 = 8944\ см^{2}.\]
\[Ответ:\ 8944\ см^{2}.\]