Speed of the boat in still water = (Downstream speed of boat + Upstream speed of boat)/2 ⇒ Speed of the boat in still water = (14 + 10)/2 = 12 km/h ⇒ Time = Distance/speed ⇒ Time = 72/12 = 6 hours ∴ The boat can cover 72 km in 6 hours in still water.