Supposing that telegraph poles on a railroad are $50 \, m$ apart,how many will be passed by a train in $4 \, hours$ if the speed of the train is $45 \, km/h$?

$A$ person has to reach a certain place at a certain time. He finds that he will be $15 \text{ minutes}$ late if he walks at $4 \text{ km/h}$,and $10 \text{ minutes}$ earlier if he walks at $6 \text{ km/h}$. How far has he to walk? (in $\text{km}$)

By walking at $\frac{3}{4}$ of his usual speed,a man reaches his office $20 \text{ minutes}$ later than usual. His usual time is (in $\text{minutes}$):

$A$ train $200 \, m$ long is running at a speed of $20 \, m/s$. In how much time (in $seconds$) will it cross a bridge of $400 \, m$ length?

$A$ train $300 \ m$ long is running with a speed of $54 \ km/h$. In what time will it cross a telephone pole? (in $seconds$)

$A$ train $180 \, m$ long is running at a speed of $90 \, km/h$. How long will it take to pass a post? (in $sec$)