A particle moves according to a law of motion s= f(t), t20, where t is measured in seconds and s in feet. f(t)=3-12t2 + 36t (a) Find the velocity at time t. v(t)- 31-24t+36 (b) What is the velocity after 4 s? v(4)=-12 ft/s (c) When is the particle at rest? (Enter your answer as a comma-separated list.) t=2,6 (d) When is the particle moving in the positive direction? (Enter your answer in interval notation.) t = (0,6) X (e) Find the total distance traveled during the first 8 s. 96 ft