How many $km/h$ does a man walk who passes through a street $600 \, m$ long in $5 \, minutes$?

$A$ starts from a place $P$ to go to a place $Q$. At the same time $B$ starts from $Q$ to $P$. If after meeting each other $A$ and $B$ took $16$ and $25$ $hours$ more respectively to reach their destinations,the ratio of their speeds is

$A$ train is travelling at a rate of $45 \, km/hr$. How many seconds will it take to cover a distance of $\frac{4}{5} \, km$?

Two trains are running in opposite directions with the same speed. If the length of each train is $135 \, m$ and they cross each other in $18 \, s$,the speed of each train is (in $km/h$):

$A$ thief is stopped by a policeman from a distance of $150\, m$. When the policeman starts the chase,the thief also starts running. Assuming the speed of the thief as $7\, km/h$ and that of the policeman as $9\, km/h$,how far would the thief have run before he is overtaken by the policeman? (in $m$)

$A$ motorcyclist left $6 \frac{2}{3}$ minutes later than the scheduled time,but in order to reach his destination $21 \, km$ away on time,he had to increase his speed by $12 \, km/h$ from his usual speed. What is the usual speed (in $km/h$) of the motorcyclist?