A train running at 25 km/hr takes 18 seconds to pass a platf

A train running at 25 km/hr takes 18 seconds to pass a platform. Next, it takes 12 seconds to pass a man walking at 5 km/hr in the same direction. Find the length of the train and that of the platform.

Distance = Speed*time
It's probably best to convert to meters so we can find the length of the platform.
Distance = 25000 meters/h * 18 seconds*(1/60*60)
Distance =(25000*18 / [3600] ) = 125m

I'm not sure how we take the length of the train into account (if we do at all) to solve this problem. For example, If we were measuring by the time the very front of the train passed one end of the platform to the time the very front of the train passed the other end, the result would be different than if we counted when the very front of the train passed one end of the platform to the time the back side of the train passed the end.

As for the problem involving the man, the man is moving forward at a speed of 5km/h while the train is moving forward at a speed of 25km/h. Therefore, the train is moving past the man at a total speed of 20km/h.

distance = speed * time
distance = 20km/h * 12 seconds
distance (length of train) = 66.6 m

We know the length of the train is roughly 66.6m and the distance covered passing the platform was 125m. However, The platform isn't 125m long - it is 125m minus the length of the train long (or so I think) which is 125-66.6 or roughly 59m. Both of these answers are in A so I think that is the right answer. I am still having a bit of trouble conceptualizing why we have to subtract out the length of the train, however.

ANSWER: a) 200/3m & 175/3m