please help fast!

Of the five quadratics listed below, four of them have two distinct roots. The fifth quadratic has a repeated root. Find the value of the repeated root.
\begin{align*}
&-x^2 + 18x + 81 \\
&3x^2 - 3x - 168 \\
&x^2 - 4x - 4 \\
&25x^2 - 30x + 9 \\
&x^2 - 14x + 24
\end{align*}