1. At $12: 00$ a raft departed from point A to point B, located downstream along the river. At $12: 45$ a motorboat departed from A in pursuit of the raft, caught up with the raft at 13:00, and continued its journey. Upon arriving at point B, the boat turned around and headed back, meeting the raft at 14:00. Determine the time of the raft's arrival at point B.
Answer: 15:00. Solution. The boat caught up with the raft in 15 minutes, which means its speed downstream is 4 times the speed of the river current. If we consider a coordinate system associated with the raft, it is not difficult to understand that the boat arrived at point B at 13:30, i.e., spent 45 minutes traveling from A to B. Accordingly, the raft will take 4 times longer and arrive at $15-00$.