nomor 21 bagaimana yaa?? tolong yaa, pakai caraa :))

Vo = 10 m/s
Vt = 20 m/s
s = 100 m
t = ___?

s = (1/2)(Vt + Vo).t
100 = (1/2)(20 + 10).t
100 = 15.t
    t = 6,7 s ← jawab : D