When you rearrange the formula, you are able to get it into the form [math]ax^2 + bx + c =0[/math]. [math]s = {v_0}t + \frac{1}{2}at^2 \rightarrow \frac12 at^2 + {v_0}t - s = 0[/math]. This implies:
[math]a = \left(\frac12 a\right), \ b={v_0}, \ c={-s}[/math].
For these type of formula, known as the quadratic equation (Highest power is 2), you can use the quadratic equation to find the value of [math]x[/math]. The quadratic formula is:
[math]x= \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}[/math]