$\begin{equation*} \begin{cases} 5(x + 2y) - 3 = x + 5 &\\ y + 4(x - 3y) = 50 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 5x + 10y - 3 = x + 5 &\\ y + 4x - 12y = 50 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 5x + 10y - x = 5 + 3 &\\ 4x - 11y = 50 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 4x + 10y = 8 &\\ 4x - 11y = 50 & \end{cases} \end{equation*}$
4x + 10y − (4x − 11y) = 8 − 50
4x + 10y − 4x + 11y = −42
21y = −42
y = −2
4x − 11 * (−2) = 50
4x + 22 = 50
4x = 50 − 22
4x = 28
x = 7
Ответ: x = 7, y = −2.

$\begin{equation*} \begin{cases} 2,5(x - 3y) - 3 = -3x + 0,5 &\\ 3(x + 6y) + 4 = 9y + 19 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 2,5x - 7,5y - 3 = -3x + 0,5 &\\ 3x + 18y + 4 = 9y + 19 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 2,5x + 3x - 7,5y = 0,5 + 3 &\\ 3x + 18y - 9y = 19 - 4 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 5,5x - 7,5y = 3,5 &\\ 3x + 9y = 15 |:3 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 5,5x - 7,5y = 3,5 |*2 &\\ x + 3y = 5 |*5 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 11x - 15y = 7 &\\ 5x + 15y = 25 & \end{cases} \end{equation*}$
11x − 15y + 5x + 15y = 7 + 25
16x = 32
x = 2
2 + 3y = 5
3y = 5 − 2
3y = 3
y = 1
Ответ: x = 2, y = 1.