The position of a point which moves in a straight line is given by x = bt3 - ct where x is in metre, t in second and b and c are positive constants. when t = 2 second, the acceleration is 24 m/s2 in positive x direction and at the same time, the velocity is 8 m/sec in negative x direction. Find the total time t required for the point to return to the origin at x = 0