As the comments state, the velocity is the derivative of the position.
Therefore, the velocity as function of time is:
ds / dt = 24 + 6t - 3t^2.
That is a parabola whose maximum is (1,27). With that you know that the velocity will never be either 63 m/s or 81 m/s.
Also, you know that the velocity at t = 1 s is 27 m/s.
And, you can also find that the velocity at t = 3 is 15 m/s.
I am confident on that this analysis solves your question. Else, insert a comment.