Two trains of equal length take $10 \, s$ and $15 \, s$ respectively to cross a telegraph post. If the length of each train is $120 \, m$,in what time (in $s$) will they cross each other while travelling in the same direction?

$A$ train $150 \, m$ long takes $20 \, s$ to cross a platform $450 \, m$ long. The speed of the train in $km/h$ is:

$A$ man walks a certain distance and rides back in $4 \, h \, 30 \, min$. He could ride both ways in $3 \, h$. The time required by the man to walk both ways is?

$A$ car travels a distance of $75 \, km$ at the speed of $25 \, km/h$. It covers the next $25 \, km$ of its journey at the speed of $5 \, km/h$ and the last $50 \, km$ of its journey at the speed of $25 \, km/h$. What is the average speed of the car? (in $km/h$)

$A$ passenger train running at the speed of $80 \text{ km/h}$ leaves the railway station $6 \text{ hours}$ after a goods train leaves and overtakes it in $4 \text{ hours}$. What is the speed of the goods train? (in $\text{km/h}$)

Two men start together to walk a certain distance,one at $4 \, km/h$ and another at $3 \, km/h$. The former arrives half an hour before the latter. Find out the distance in $km$.