Two donkeys are standing $400 \, m$ apart. The first donkey can run at a speed of $3 \, m/s$ and the second can run at $2 \, m/s$. If both donkeys run towards each other, after how much time (in $seconds$) will they meet?

$A$ 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 $s$)

$A, B$ and $C$ start together from the same place to walk around a circular path of length $12 \, km$. $A$ walks at the rate of $4 \, km/h$,$B$ at $3 \, km/h$,and $C$ at $\frac{3}{2} \, km/h$. They will meet together at the starting place at the end of (in $h$):

Robert is travelling on his cycle and has calculated to reach point $A$ at $2\, p.m.$ if he travels at $10 \,km/hr$; he will reach there at $12\, noon$ if he travels at $15\, km/hr$. At what speed must he travel to reach $A$ at $1\, p.m.$? (in $km/hr$)

$A$ student walks from his house at $5 \, km/h$ and reaches his school $10 \, minutes$ late. If his speed had been $6 \, km/h$,he would have reached $15 \, minutes$ early. The distance of his school from his house is (in $km$):

$A$ walks around a circular field at the rate of one $round/hour$,while $B$ runs around it at the rate of six $rounds/hour$. They start in the same direction from the same point at $7.30 \, a.m$. They shall first cross each other at (in $a.m.$)