let the whole distance be h covered in time t then the distance covered in time (t1) sec will be h 9h/25 = 16h/25.
Now apply the formula s = ut + (1/2)gt^2 at time t and (t1)
In time t
h = (1/2)gt^2 ..........( u being zero )
In time (t1)
16h/25 = (1/2) g(t1)^2
Devide the first eq by second one, find t and then find h using any of the two eqs.
