S(t)=-4.9+vt+s. to estimate the height of a building, a stone is dropped from the top of the building into a pool of water at ground level. how high is the building if the splash is seen 5.6 seconds after the stone is dropped?

The height of a falling object can be approximated (assuming no air resistance) by
  h(t) = -16t^2 + h0
where h0 is the initial height of the object.
We are given h(5.6) = 0 and are asked to find h0.
  0 = -16*5.6^2 + h0
  16*5.6^2 = h0
  501.76 = h0
The height of the building is about 500 ft.

Whose mistake? can you give more details to what the question is asking?