$A + B = \left[ {\begin{array}{*{20}{c}}
2&3\\
5&{ - 1}
\end{array}} \right]\,\,\,\,\,\,\,\,....\left( 1 \right)$

$A' + B' = \left[ {\begin{array}{*{20}{c}}
2&5\\
3&{ - 1}
\end{array}} \right]\,\,\,$

$A - B = \left[ {\begin{array}{*{20}{c}}
2&5\\
3&{ - 1}
\end{array}} \right]\,\,\,\,\,\,\,\,.....\left( 2 \right)$

After addding equation $(1)$ and $(2)$

$A = \left[ {\begin{array}{*{20}{c}}
2&4\\
4&{ - 1}
\end{array}} \right]\,,B = \left[ {\begin{array}{*{20}{c}}
0&{ - 1}\\
1&0
\end{array}} \right]\,$

$AB = \left[ {\begin{array}{*{20}{c}}
4&{ - 2}\\
{ - 1}&{ - 4}
\end{array}} \right]$