Correct Answer - Option 2 : 6

**Given:**

Speed of Dolphin in still water = 15 km/h

Speed of the stream = 4 km/h

Distance covered in downstream = 114 km

**Formulas Used:**

Time = Distance/Speed

S_{(downstream)} = S_{(boat)} + S_{(stream)}

**Calculation:**

S_{(downstream)} = S_{(boat)} + S_{(stream)}

⇒ S_{(downstream)} = (15 + 4) km/h

⇒ S_{(downstream)} = 19 km/h

Time = Distance/Speed

⇒ T = 114/19 h

⇒ T = 6 h

**∴** **The time taken by dolphin to cover 114 km distance in downstream is 6 hours**