\textbf{158-} The equation of motion of a particle in SI is $x = \dfrac{2}{3}t^3 - 6t^2 + 20t$. What is the minimum speed (in meters per second) that this particle reaches along its path?
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(1) zero \hfill (2) $1$ \hfill (3) $2$ \hfill (4) $4$
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