\[x^{2} + bx - 30 = 0;\ \ \ x_{1} = 6\]
\[\left\{ \begin{matrix} x_{1} + x_{2} = - b \\ x_{1} \cdot x_{2} = - 30 \\ \end{matrix} \right.\ \]
\[1)\ 6 \cdot x_{2} = - 30\ \ \]
\[x_{2} = - 5.\]
\[2)\ 6 + ( - 5) = - b\ \ \]
\[1 = - b\]
\[b = - 1.\]
\[Ответ:\ \ x_{2} = - 5;\ \ b = - 1.\]