Question 896685
Lets find the distance.

{{{3*10 = 30}}} km

Velocity of the boat against current = 30/4 kph

Boat velocity with current = Boat velocity (V) + current velocity (C)

{{{10 = V + C}}}

And against current ..

{{{30/4 = V - C}}}

Add both equations

{{{10 +30/4 = 2V}}}

{{{70/4 = 2V}}}

{{{V = 70/8 = 8.75}}} kph