A traveler at 10:25

Explanation, because we set off at 10:15 and return at 13:00, we have 2 hours and 45 minutes,

and we have to rest for 15 minutes every 30 minutes, so The equivalent of traveling in a small boat is only 2 hours

And tourists can only return after a certain break, but the water flow is not static, so the distances traveled upstream and upstream in the same time are also different. , so it is only possible to go downstream for up to 30 minutes

So the maximum distance is

0.5x(3+1.4)=2.1 kilometers

Verifiable: The countercurrent time is

2.1/(3-1.4) less than 1.5

So we must be able to get back before 13:00