The positions of two intergalactic spaceships are given at any moment t by: ri = [3 . t-5, -1, 5 . 1-5] and 12 = [3 . t+ 2, 2 . 1 - 5, 5 . t+ 2] where all units are intergalactic units. Find the moment of time when the spaceships are closest. Moment = Note. Enter the answer as a rational number. Example: 3/4