\[x^{2} - 13x + q = 0;\ \ \ x_{1} = - 7.\]
\[\left\{ \begin{matrix} x_{1} + x_{2} = 13 \\ x_{1} \cdot x_{2} = q\ \ \ \\ \end{matrix} \right.\ \]
\[- 7 + x_{2} = 13 \Longrightarrow x_{2} = 20.\]
\[- 7 \cdot 20 = q \Longrightarrow q = - 140.\]
\[Ответ:\ q = - 140;\ \ \ x_{2} = 20.\]