$A$ $135\, m$ long train is running with a speed of $54\, km/h$. In what time will it pass a telegraph post? (in $seconds$)

In a $1 \, km$ race,$A, B$,and $C$ are three participants. $A$ can give $B$ a start of $50 \, m$ and $C$ a start of $69 \, m$. The start,which $B$ can allow $C$ is (in $m$):

$A$ and $B$ run a kilometer and $A$ wins by $25 \, s.$ $A$ and $C$ run a kilometer and $A$ wins by $275 \, m.$ When $B$ and $C$ run the same distance,$B$ wins by $30 \, s.$ The time taken by $A$ to run a kilometer is?

$A$ passenger train $150 \ m$ long is travelling with a speed of $36 \ km/h$. If a man is cycling in the direction of the train at $9 \ km/h$,then the time taken by the train to pass the man is? (in $s$)

Two trains of lengths $120 \,m$ and $80 \,m$ are running in the same direction with velocities of $40 \,km/h$ and $50 \,km/h$ respectively. The time taken by them to cross each other is (in $sec$).

$A$ person goes from point $A$ to $B$ with a speed of $55 \text{ km/hr}$ and returns with a speed of $65 \text{ km/hr}$. What is the average speed (in $\text{km/hr}$) of the person while going and coming back from $A$ to $B$?