$A$ man goes from $A$ to $B$ at a uniform speed of $12 \, km/h$ and returns with a uniform speed of $4 \, km/h$. His average speed (in $km/h$) for the whole journey is?

Two persons begin together to write out a booklet containing $8190$ lines. The first person starts with the first line,writing at the rate of $200$ lines an hour; and the second person starts with the last line,then writes the $8189^{th}$ line and so on,proceeding backward at the rate of $150$ lines an hour. At what time will they meet (in $.4$)? (in hours)

On a tour,a man travels at the rate of $64 \text{ km/h}$ for the first $160 \text{ km}$,then travels the next $160 \text{ km}$ at the rate of $80 \text{ km/h}$. The average speed in $\text{km/h}$ for the first $320 \text{ km}$ of the tour is:

$A$ train covers a distance between station $A$ and station $B$ in $45 \, min$. If the speed of the train is reduced by $5 \, km/h$,then the same distance is covered in $48 \, min$. The distance between stations $A$ and $B$ is? (in $km$)

The distance between places $A$ and $B$ is $999 \, km$. An express train leaves place $A$ at $6 \, am$ and runs at a speed of $55.5 \, km/h$. The train stops on the way for $1 \, hr \, 20 \, min$. It reaches $B$ at?

What is the speed of the train in $km/h$?
Statements:
$I.$ The train crosses an $x$ meter-long platform in $n$ seconds.
$II.$ The length of the train is $y$ meters.
$III.$ The train crosses a signal pole in $m$ seconds.