\[x^{2} - 4x + q = 0;\ \ x_{1} = 5\]
\[x_{1} + x_{2} = 4\]
\[5 + x_{2} = 4\]
\[x_{2} = - 1.\]
\[x_{1} \cdot x_{2} = q\]
\[q = 5 \cdot ( - 1)\]
\[q = - 5.\]
\[Ответ:x_{2} = - 1;q = - 5.\]