A particle starts at the origin and moves out along the positive x-axis for a while then stops and moves back towards the origin. The distance of the particle from the origin at the end of `t` seconds is given by `x(t)=2t^3-9t^2+12t` Find (i) the time `t_1`, when particle stops for the first time. (i)acceleration at time `t_2` when the particle stops for the seconds time