a girl wants to swim across a river 50 m wide. the river flows with a velocity of u m s-1 parallel to the banks. the girl swims at a velocity v m s^-1 . she crosses the river as quick as possible and she takes 75 seconds and she is carried down stream by 30 m. find (i) u and v (ii) how long it will take her to swim back in a straight line to her original position.

for (i) i know she heads straight across cross the river in the shortest time. to find her j direction speed which is v i ca use distance/time so v= 50/75=2/3 m s^-1

its the same for the river current so u= 30/75 =2/5m s^-1

i am not sure how to do part (ii)