Đáp án:
$\begin{array}{l}
\left\{ \begin{array}{l}
\frac{{x + y}}{3} + \frac{2}{3} = 3\\
\frac{{4x - y}}{6} + \frac{x}{4} = 1
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
\frac{{x + y + 2}}{3} = 3\\
\frac{{8x - 2y + 3x}}{{12}} = 1
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
x + y + 2 = 9\\
11x - 2y = 12
\end{array} \right.\\
\Rightarrow \left\{ \begin{array}{l}
2x + 2y = 14\\
11x - 2y = 12
\end{array} \right.\\
\Rightarrow 13x = 26\\
\Rightarrow x = 2\\
Do:x + y = 7\\
\Rightarrow y = 5
\end{array}$
Vậy x=2; y=5