\[x_{1} = - 12:\]
\[x^{2} + 115x + q = 0\]
\[\left\{ \begin{matrix} x_{1} + x_{2} = - 15 \\ x_{1} \cdot x_{2} = q\ \ \ \ \ \ \ \\ \end{matrix} \right.\ \]
\[x_{2} - 12 = - 15\ \]
\[x_{2} = - 15 + 12\ \ \]
\[x_{2} = - 3.\]
\[- 12 \cdot ( - 3) = q\ \ \ \]
\[q = 36.\]
\[Ответ:\ \ q = 36;\ \ x_{2} = - 3.\]