Answer
$$
\left[
\begin{array}{ccc|c}
1 & -4 & 2 & 3 \\
1 & -4 & 4 & 0 \\
2 & 0 & 7 & 4 \\
\end{array}
\right]
$$.
Work Step by Step
The row operation $\frac{1}{3}R_1$ means we have to multiply the entire first row of the augmented matrix by $\frac{1}{3}$. The matrix becomes$$
\left[
\begin{array}{ccc|c}
1 & -4 & 2 & 3 \\
1 & -4 & 4 & 0 \\
2 & 0 & 7 & 4 \\
\end{array}
\right]
$$.
