First, find the velocity \(v\) by differentiating the displacement \(s\) with respect to time \(t\):

\(v = \frac{ds}{dt} = 3t^2 - 12t + 4\).

Next, find the acceleration \(a\) by differentiating the velocity \(v\) with respect to time \(t\):

\(a = \frac{dv}{dt} = 6t - 12\).

Set the acceleration to zero to find the time \(t\) when the acceleration is zero:

\(6t - 12 = 0\)

\(t = 2\).

Substitute \(t = 2\) into the velocity equation to find the velocity at this time:

\(v = 3(2)^2 - 12(2) + 4 = 12 - 24 + 4 = -8 \text{ ms}^{-1}\).