\[
\text{How to solve a system equation?}
\]
\begin{align}
x + 2y = 2 \tag{g} \\
3x +4y = 2 \tag{f}
\end{align}
\begin{equation}
\begin{aligned}
\text{Let solve the equation} \\
& x + 2y = 2 \label{3}\\
& \Rightarrow x = 2 - 2y \\
& \Rightarrow 3(2-2y) + 4y = 2 \\
& \Rightarrow 6 - 6y + 4y = 2 \\
& \Rightarrow 6 - 2y = 2 \\
& \Rightarrow \color{red}{y = 2} \\
& \text{ Sub }y = 2 \text{ into } x = 2-2y \\
& \Rightarrow x = 2 - 2 \times 2 \\
& \Rightarrow \color{red}{x = -2} \\
& \text{Therefore we have } \\
& \left[
\begin{array}{c}
x \\
y
\end{array}
\right] =
\left[
\begin{array}{c}
-2 \\
2
\end{array}
\right] \\
\text{We can check our solution} \\
& -2 + 2(2) = 2 \\
& 3(-2) + 4(2) = 2
\end{aligned}
\end{equation}