A ship S is moving along a straight line with constant velocity. At time t hours the position vector of S is s km. When t = 0, s = 9i − 6j. When t = 4, s = 21i 10j. Find (a) the speed of S, (4) (b) the direction in which S is moving, giving your answer as a bearing. (2) (c) Show that s = (3t 9)i (4t − 6)j.