A man in a train notices that he can count 21 telephone posts in one minute. If they are known to be 50 metres apart, then at what speed is the train travelling?

Quantity$1$: Train A is running at a speed of $25 \mathrm{m}/\sec$ crosses. Train B is coming from opposite direction running at a speed of $15 \mathrm{m}/\sec$ in $12$ seconds. Length of Train A is twice of Train B. Find the length of train A.

Quantity $2$: $160$ Meters.

The speeds of John and Max are $30 km/h$ and $40 km/h$. Initially, Max is at a place L and John is at a place M. The distance between L and M is $650 km$. John started his journey $3$ hours earlier than Max to meet each other. If they meet each other at a place P somewhere between L and M, then the distance between P and M is how much?

Train A, travelling at $\mathrm{S} \mathrm{m}/\mathrm{s}$, can cross a platform double its length in $21$ seconds. The same train, travelling at $\mathrm{S}+5 \mathrm{m}/\mathrm{s}$, can cross the same platform in $18$ seconds. What is the value of $\mathrm{S}$?

An object travels $20$ meters in $4$ seconds and $15$ meters in the next two seconds. What is the average speed of the object?