Correct option is B
Given:
Speed of boat in still water = 13 km/h
Speed of stream = 4 km/h
Formula Used:
Upstream speed = (Speed of the boat) - (Speed of the stream)
Time = Distance/Speed
Solution:
Speed of boat in upstream = (13 – 4 ) = 9 km/h
Time taken by boat to cover 68 km upstream = 68/9 = 7 hours + 5/9 hour