(a) If the position of a particle is given by x - 20t - 5t3, where x is in meters and t is in seconds, when, if ever, is the particle's velocity zero?

(b) When is its acceleration a zero?

(c) For what time range (positive or negative) is a negative?

(d) Positive?

(e) Graph x(r) ,v(t), and a(t).