A boat takes 4 hours to travel from place a to b downstream and back from b to a upstream. If the distance from a to b is 10.5 km and the speed of the current is 9 km/h, then the speed of the boat in still water, in km/h is?

12

Let speed of boat = U km/hr.

ATQ,

        \(\frac{10.5}{U + 9}\) + \(\frac{10.5}{U - 9}\) = 4

Go through option or solve it

           U = 12 km/hr.