How long does it take for a raft floating down the river to travel 15 km if the current velocity is 0.5 m/s?

It would take 30,000 seconds, or 8 hours and 20 minutes, for a raft to travel 15 km downstream with a current velocity of 0.5 m/s. This is because the distance (15 km) divided by the velocity (0.5 m/s) equals the time (30,000 seconds). To convert this to hours and minutes, divide the total seconds by 60 to get the total minutes (500 minutes), then divide again by 60 to get the total hours (8.33 hours). Finally, round down to the nearest whole hour (8 hours) and calculate the remaining minutes (20 minutes). Therefore, it would take 8 hours and 20 minutes for a raft to travel 15 km downstream with a current velocity of 0.5 m/s.