With the provided data you can't find a single solution, you'll have to deal with a parametric one. This is what you can do:
$s(t) = \frac{1}{2}at^2$
$\dot{s}(t) = at$
From these 2, we can get the time:
$220 = at \Rightarrow t = \frac{220}{a}$
so, the solution is
$s(\frac{220}{a}) = \frac{220^2}{2a} = \frac{24200}{a}$