The equation of motion is given for a particle by $s(t)= t^4-4t^3+3$ where $s$ is in meters, and $t$ is in seconds. Find:
(a) The first (positive) instant when the acceleration is zero.
(b) The displacement at this time.
(c) The velocity at this time.

(a) $s$
(b) $m$
(c) $m/s$