A particle is moving with acceleration given by a(t)=6t-12 and an initial velocity of 9 m/s. (a) Find the velocity of the particle at time t. (b) Find the velocity of the particle after 3 seconds. (c) When is the particle at rest? (d) When is the particle moving in the positive direction? (e) Find the total displacement of the particle during the first 8 seconds.