A spaceship is traveling through deep space with the following velocity vector as a function of time: = (2t + 4t+ 6t k) m/s, where t is in seconds. Given the initial position of the spaceship is To= (20 - 50 - 100 k) m, at what time is the spaceship the closest to the origin? Also, what is the acceleration of the spaceship at this instant? Express the acceleration in Cartesian vector form.