The function s(t) describes the motion of a particle along a line. s(t) = 6+3 - 32t + 6 (a) Find the velocity function v(t) of the particle at any time t 2 0. v(t) : (b) Identify the time interval(s) on which the particle is moving in a positive direction. (Enter your answer using interval notation.) (c) Identify the time interval(s) on which the particle is moving in a negative direction. (Enter your answer using interval notation. ) (d) Identify the time(s) at which the particle changes direction. (Enter your answers as a comma-separated list.) t =