The complex number $2+4i$ is one of the roots to the quadratic equation $x^2+bx+c=0$ where $b$ and $c$ are real numbers. The values of $b$ and $c$ are

Question

$\begin{array}{1 1} (a)\;b=4\;;\;c=20 \\ (b)\;b=4\; ; \;c=-20 \\ (c)\;b=-4\;;\;c=20 \\(d)\;b=-4\;;\;c=-20\end{array}$