Answer
$\left[ {\begin{array}{ccccccccccccccc}1&2&3\\4&5&6\\7&8&9\end{array}} \right]$, $\left[ {\begin{array}{ccccccccccccccc}9&8&7\\6&5&4\\3&2&1\end{array}} \right]$; $\left[ {\begin{array}{ccccccccccccccc}{10}&{10}&{10}\\{10}&{10}&{10}\\{10}&{10}&{10}\end{array}} \right]$
Work Step by Step
Let two matrices of order $3$$ \times 3$ be $\left[ {\begin{array}{ccccccccccccccc}1&2&3\\4&5&6\\7&8&9\end{array}} \right]$ and $\left[ {\begin{array}{ccccccccccccccc}9&8&7\\6&5&4\\3&2&1\end{array}} \right]$.
Add the matrices.
$$\begin{aligned}\left[ {\begin{array}{ccccccccccccccc}1&2&3\\4&5&6\\7&8&9\end{array}} \right] + \left[ {\begin{array}{ccccccccccccccc}9&8&7\\6&5&4\\3&2&1\end{array}} \right] &= \left[ {\begin{array}{ccccccccccccccc}{1 + 9}&{2 + 8}&{3 + 7}\\{4 + 6}&{5 + 5}&{6 + 4}\\{7 + 3}&{8 + 2}&{9 + 1}\end{array}} \right]\\ &= \left[ {\begin{array}{ccccccccccccccc}{10}&{10}&{10}\\{10}&{10}&{10}\\{10}&{10}&{10}\end{array}} \right]\end{aligned}$$
