$A$ train $75 \; m$ long overtook a person who was walking at the rate of $6 \; km/h$ and passed him in $7 \frac{1}{2}$ seconds. Subsequently,it overtook a second person,and passed him in $6 \frac{3}{4}$ seconds. At what rate (in $km/h$) was the second person travelling?

Two trains running at the rate of $45 \; km/h$ and $36 \; km/h$ respectively,on parallel tracks in opposite directions,are observed to pass each other in $8 \; seconds$. When they are running in the same direction at the same rate as before,a person sitting in the faster train observes that he passes the other in $30 \; seconds$. Find the length of the trains (in $m$).

Two trains $250 \; m$ and $200 \; m$ long are running on parallel tracks at the rate of $36 \; km/hr$ and $45 \; km/hr$ respectively. In how much time (in $sec$) will they cross each other,if they are running in the same direction?

Length of a train and that of a platform are equal. If with a speed of $135 \; km/hr$,the train crosses the platform in $40 \; seconds$,then the length (in $m$) of the train is:

$A$ train $280 \; m$ long, running with a speed of $63 \; km/hr$, will pass a tree in (in $sec$):

$A$ train $120 \; m$ long moving at a speed of $60 \; km/hr$ crosses a train $130 \; m$ long coming from the opposite direction in $6 \; seconds$. The speed of the second train is (in $km/hr$):