can you help me to isolate the ''t'' in this formula.

d=V1t+1/2at^2

pls help

d = V1*t + 0.5at^2 = 0,

Factor out t:
t(V1 + 0.5at) = 0,
t = 0.

V1 + 0.5at = 0.
0.5at = -V1,
t = -Vi / 0.5a.

This Quadratic Eq has 2 solutions:
t = o, and t = -V1 / 0.5a.