$\begin{equation*} \begin{cases} 2x + 3y = 20 &\\ 3x - 5y = 11 &\\ x + y = 9 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 2x + 3y = 20 &\\ 3x - 5y = 11 &\\ x = 9 - y & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 2(9 - y) + 3y = 20 &\\ 3(9 - y) - 5y = 11 &\\ x = 9 - y & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 18 - 2y + 3y = 20 &\\ 27 - 3y - 5y = 11 &\\ x = 9 - y & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} y = 20 - 18 &\\ -8y = 11 - 27 &\\ x = 9 - y & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} y = 2 &\\ -8y = -16 &\\ x = 9 - y & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} y = 2 &\\ y = 2 &\\ x = 9 - 2 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} y = 2 &\\ y = 2 &\\ x = 7 & \end{cases} \end{equation*}$
Ответ: прямые проходят через точку (7;2).