1) s=ut+0.5at^2
2) v^2=u^2+2as
3) s=ut+0.5at^2
4) s=ut+0.5at^2 [rearrange]
5) s=ut+0.5at^2 [rearrange, solve resulting quadtratic equation (in t) using quadratic formula, only accepting the positive value]
6) s=ut+0.5at^2
NOTE: Here i have used common physics notation, and additionally...