Correct Answer - Option 2 : 6.75 km/hr

**Concept Used:**

Speed = Distance/Time

**Calculation:**

Suppose he rows 15 km downstream and 12 km upstream in x hours.

Speed_{(upstream) }= 12/x km/hr and Speed_{(downstream)} = 15/x km/hr

It is given that he can row to a place 60 km distant and back in 18 hours.

⇒ 60/(12/x) + 60/(15/x) = 18

⇒ 5x + 4x = 18

⇒ x = 2

Speed_{(upstream) }= (12/x) km/hr = 12/2 = 6 km/hr

Speed_{(downstream)} = (15/x) km/hr = 15/2 = 7.5 km/hr

**∴ Speed of boat = ½(6 + 7.5) = 6.75 km/hr **