Answer :
Half of 72 is 36. If you divided 36 by 4, you would get 9. So, s = 9 and means that it takes 9 seconds for the rock to be sunk half way.
Half of 72 is 36. If you divided 36 by 4, you would get 9. So, s = 9 and means that it takes 9 seconds for the rock to be sunk half way.