$A$ car starts with a speed of $70 \, km/h$ and its speed increases by $10 \, km/h$ every two hours. In how many hours will it cover $345 \, km$?

$A, B$ and $C$ start at the same time in the same direction to run around a circular stadium. $A$ completes a round in $252 \text{ seconds}$,$B$ in $308 \text{ seconds}$ and $C$ in $198 \text{ seconds}$,all starting at the same point. After what time will they next meet at the starting point again?

$A$ man goes from a place $A$ to $B$ at a speed of $12 \, km/hr$ and returns from $B$ to $A$ at a speed of $18 \, km/hr$. The average speed for the whole journey is (in $km/hr$):

Two men $A$ and $B$ start from a place $P$ walking at $3 \, km/h$ and $3.5 \, km/h$ respectively. How many $km$ will they be apart at the end of $3 \, h$,if they walk in opposite directions (in $.5$)?

Ravi and Ajay start simultaneously from a place $A$ towards $B$,$60 \, km$ apart. Ravi's speed is $4 \, km/h$ less than that of Ajay. Ajay,after reaching $B$,turns back and meets Ravi at a place $12 \, km$ away from $B$. Ravi's speed is (in $km/h$):

$A$ car travels $10\, m$ in $1$ second. Find its speed in $km/h$.