a) Towards each other d = s - t*(R + F) b) In opposite directions d = s + t*(R + F) c) In the same direction if the first is slower Unclear. Depends on what is this "the same" direction: there are two "the same directions". d) In the same direction if the first is faster Unclear. Same notice as the previous.
s distance between piers R and F speeds of each boat t travel time d distance between boats