\(\left[ {\begin{array}{*{20}{c}}4&6\\{ - 2}&8\end{array}} \right]\)

\begin{aligned}
2 A&=2 \times\left[\begin{array}{cc}
2 & 3 \\
-1 & 4
\end{array}\right]\\
&=\left[\begin{array}{ll}
2 \times 2 & 2 \times 3 \\
2 \times -1 & 2 \times 4
\end{array}\right] \\
&=\left[\begin{array}{cc}
4 & 6 \\
-2 & 8
\end{array}\right]
\end{aligned}