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.**