\( \left[ {\begin{array}{*{20}{c}}7&10\\3&{3}\end{array}} \right]\)

\begin{aligned}
A+B &=\left[\begin{array}{cc}
4 & 3 \\
2 & -1
\end{array}\right]+\left[\begin{array}{ll}
3 & 7 \\
2 & 4
\end{array}\right] \\
&=\left[\begin{array}{cc}
4+3 & 3+7 \\
2+2 & -1+4
\end{array}\right] \\
&=\left[\begin{array}{cc}
7 & 10 \\
4 & 3
\end{array}\right]
\end{aligned}