Answer:
t=4h
Steps below
Step-by-step explanation:
We know:
speed of boat with respect to earth: 13 km
speed of stream with respect to earth: 4 km
13 km/h + 4 km/h = 17 km/h The time to travel 68 km with this speed is thus t = 68 km 17 km h = 4 h
Hope this helps.
