Two boats, $A$ and $B$, having same speed relative to the river, are moving in a river. Boat $A$ moves normal to the river current, as observed by an observer, moving with the velocity of the river current. Boat$B$ moves normal to the river, as observed by an observer on the ground.

Two trains, which are moving along different tracks in opposite directions towards each other, are put on the same track due to a mistake. Their drivers, on noticing the mistake, start slowing down the trains when the trains are $300 \mathrm{m}$ apart. Graphs given below show their velocities as a function of time as the trains slow down. What is the separation between the trains (in metre) when both have stopped?