[tex]
s=\dfrac{1}{2}gt^2\:\:\:\mathrm{divide\:both\:sides\:by\:t^2} \\
\dfrac{s}{t^2}=\dfrac{1}{2}g\:\:\:\mathrm{divide\:both\:sides\:by\:1/2} \\
\dfrac{\frac{s}{t^2}}{\frac{1}{2}}=g\:\:\:\mathrm{simplify} \\
g=\boxed{\dfrac{2s}{t^2}}
[/tex]
Hope this helps.
