Answer
\begin{align*} x&=-5 &\text{ and }& &x=35\end{align*}
Work Step by Step
Subtract $400$ from each side to obtain:
$$x^2-30x-175=0$$
Factor the trinomial to obtain:
\begin{align*}
(x-35)(x+5)&=0\\
\end{align*}
Use the Zero-Product Property by equating each factor to zero, then solve each equation to obtain:
\begin{align*}
x-35&=0 &\text{or}& &x+5=0\\
x&=35 &\text{or}& &x=-5
\end{align*}
