4x+y=5 ;x+y=1 ????? aking first-degree equations with two unknowns ?
$$\small{\text{$
\begin{array}{lccrcl}
(1)&:& & 4x + y &=& 5 \\
(2)&:& & x + y &=& 1 \\
\hline
&\\
(1) - (2)&:& & 4x - x + y - y &=& 5-1\\
& & & 3x &=& 4 \qquad |\qquad : 3\\
& & & \textcolor[rgb]{1,0,0}{x} &\textcolor[rgb]{1,0,0}{=}& \textcolor[rgb]{1,0,0}{ \frac{4}{3} }\\
\hline
&\\
(2)&:& & x + y &=& 1 \\
& & & \frac{4}{3} +y &=& 1 \qquad |\qquad -\frac{4}{3}\\
& & & y &=& 1 -\frac{4}{3} \\
& & & \textcolor[rgb]{1,0,0}{y} &\textcolor[rgb]{1,0,0}{=}& \textcolor[rgb]{1,0,0}{-\frac{1}{3}} \\
\end{array}
$}}$$