What is the length of the bridge (in $m$) that a man riding at $15 \, km/h$ can cross in $5 \, minutes$?

$A$ bicycle rider covers his onward journey from $A$ to $B$ at $10 \text{ km/h}$ and during the return journey from $B$ to $A$ he covers the same distance at $8 \text{ km/h}$. If he finishes the onward and return journey in $4 \frac{1}{2} \text{ hours}$,then the total distance covered by him during the entire journey is (in $\text{km}$)

$A$ train,$300 \, m$ long,passes a man walking along the line in the same direction at the rate of $3 \, km/h$ in $33 \, s$. The speed of the train is (in $km/h$):

$A$ boy rides his bicycle $10 \, km$ at an average speed of $12 \, km/hr$ and again travels $12 \, km$ at an average speed of $10 \, km/hr$. His average speed for the entire trip is approximately (in $km/hr$)

Two guns were fired from the same place at an interval of $13 \text{ minutes}$,but a person in a train approaching the place hears the second shot $12 \text{ minutes } 30 \text{ seconds}$ after the first. Find the speed of the train,assuming that sound travels at $330 \text{ m/s}$ (in $\text{km/hr}$).

$A$ 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 $B$?