A body has a velocity of 72 km/hr. Find its value in m/s.

What you want to do is do unit analysis. There are 3600s in one hour and 1000m in 1km.

72km/h * 1h/3600s * 1000m/1km

this way the hours should cancel out and the km should cancel out leaving you with m/s

so 72/3600 * 1000 gives you 21.11m/s