What is the length of the bridge (in $m$) that a man riding at $15 \, km/h$ can cross in $5 \, minutes$?

Two trains,Kanpur Mail and Delhi Mail,start at the same time from stations Kanpur and Delhi respectively towards each other. After passing each other,they take $12\, \text{hours}$ and $3\, \text{hours}$ to reach Delhi and Kanpur respectively. If the Kanpur Mail is moving at the speed of $48\, \text{km/hr}$,the speed of the Delhi Mail is (in $\text{km/hr}$):

$A$ person travels $600 \, km$ by train at $80 \, km/hr$,$800 \, km$ by ship at $40 \, km/hr$,$500 \, km$ by aeroplane at $400 \, km/hr$,and $100 \, km$ by car at $50 \, km/hr$. What is the average speed for the entire distance? (in $km/hr$)

$A$ train $300 \text{ m}$ long is running at a speed of $90 \text{ km/h}$. How many seconds will it take to cross a $200 \text{ m}$ long train running in the opposite direction at a speed of $60 \text{ km/h}$?

$A$ thief is noticed by a policeman from a distance of $200\, m$. The thief starts running and the policeman chases him. The thief and the policeman run at the speed of $10\, km/h$ and $11\, km/h$ respectively. What is the distance between them after $6\, minutes$? (in $m$)

Two trains start at the same time from Mumbai and Pune and proceed towards each other at the speeds of $60\, km/h$ and $40\, km/h$, respectively. When they meet, it is found that one train has travelled $20\, km$ more than the other. Find the distance between Mumbai and Pune (in $km$).