$\begin{equation*} \begin{cases} \frac{y + 1}{3x - 4} = \frac{1}{2} &\\ \frac{5x + y}{3x + 11} = 1 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 2y + 2 = 3x - 4 &\\ 5x + y = 3x + 11 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 2y - 3x = -2 - 4 &\\ 5x - 3x + y = 11 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 2y - 3x = -6 &\\ 2x + y = 11 | * (-2) & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 2y - 3x = -6 &\\ -4x - 2y = -22 & \end{cases} \end{equation*}$
2y − 3x − 4x − 2y = −6 − 22
−7x = −28
x = −28 : (−7)
x = 4
2x + y = 11
y = 11 − 2x
y = 11 − 2 * 4
y = 11 − 8
y = 3
Ответ: (4;3)

$\begin{equation*} \begin{cases} \frac{3x + 10}{y + 1} = \frac{1}{12} &\\ \frac{5x + y}{9x + 2y} = \frac{4}{5} & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 12(3x + 10) = y + 1 &\\ 5(5x + y) = 4(9x + 2y) & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 36x + 120 = y + 1 &\\ 25x + 5y = 36x + 8y & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 36x - y = 1 - 120 &\\ 25x - 36x + 5y - 8y = 0 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 36x - y = -119 | * (-3) &\\ -11x - 3y = 0 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} -108x + 3y = 357 &\\ -11x - 3y = 0 & \end{cases} \end{equation*}$
−108x + 3y − 11x − 3y = 357
−119x = 357
x = 357 : (−119)
x = −3
−11x − 3y = 0
−3y = 11x
−3y = 11 * (−3)
−3y = −33
y = −33 : (−3)
y = 11
Ответ: (−3;11)