Answer:
Velocity, V = 3t²- 28t+6
Displacement, s = t³ - 14t²+6t -8
At t = 5.8 s
    s = -249.05 m
    v = -55.48 m/s
At t = 12.7 s
    s = -141.48 m
    v = 134.27 m/s
Explanation:
We have acceleration of a particle is given by  a = 6t - 28
Velocity
   [tex]v=\int adt=\int (6t - 28)dt=3t^2-28t+C[/tex]
At t = 0 we have vâ‚€ = 6 m/s
     v₀ = 6 =  3 x 0 ²-28 x 0+C
     C = 6
    So velocity, V = 3t² - 28t+6
Displacement
    [tex]s=\int vdt=\int (3t^2-28t+6)dt=t^3-14t^2+6t+C[/tex]
At t = 0 we have sâ‚€ = -8 m
     s₀ = -8 =  0³ + 14 x 0² + 6 x 0 + C
     C = -8
    So displacement, s = t³ - 14t²+6t -8
At t = 5.8 s
    s = 5.8³ - 14 x 5.8²+6 x 5.8 - 8 = -249.05 m
    v =  3 x 5.8² - 28 x 5.8 + 6 = -55.48 m/s
At t = 12.7 s
    s = 12.7³ - 14 x 12.7²+6 x 12.7 - 8 = -141.48 m
    v =  3 x 12.7² - 28 x 12.7 + 6 = 134.27 m/s