Make t subject of the formula: s=ut+1/2at^2.

Answer 1

use the quadratic formula. It might help to get rid of the fraction first
at^2 + 2ut - 2s = 0

t = (-2u ±√(4u^2 + 8as))/(2a)
= (-u±√(u^2+2as))/a

Answer 2

By using completing the square method amd also apply all the rule involve to it. hence, you will get
t=-u+/- sqrtu^2+2as/a