I solved the problem but I want to make sure I did it correctly.

starting at time t=0, a train is halted by a braking deceleration of , with the result that its position at time t is

show that is the train's postion when the brakes are applied and is its velocity at that time. Find the stopping distances if is

gives

and

gives

and solve s(t) to get the distance using

thus the answer is 400 metres.

ps. teaching myself LaTex