Correct Answer - Option 1 : 28 hours
Given
Speed of boat = 28 km/h
Speed of stream = 10 km/h
Formula used
Downstream speed = (Speed of boat + Speed of stream)
Upstream speed = (Spees of boat - Speed of stream)
Time = Distance/Speed
Calculation
Downstream speed = (28 + 10)
⇒ 38 km/h
Upstream speed = (28 - 10)
⇒ 18 km/h
Time = (342/38) + (342/18)
⇒ 9 + 19
⇒ 28 hours
∴ Total time taken is 28 hours.