The quadratic formula is written as:
$$x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$
The cash flow structure can be represented as:
$$
\begin{array}{r|ccccc}
\text{Inflows (+)} & & \$5,000 & \$5,000 & \$5,000 & \$5,000 \\
& & \uparrow & \uparrow & \uparrow & \uparrow \\
\text{Timeline} & 0 & 1 & 2 & 3 & 4 \\
\hline
& \downarrow & & & & \\
\text{Outflows (-)} & -\$15,000 & & & & \\
\end{array}
$$