The supplies should be droppped how many seconds before the plane is directly over the target?

Question

The pilot of an airplane traveling 180 km/h wants to frop supplies to flood victims isolated on a ppatch of land 160m below. The supplies should be droppped how many seconds before the plane is directly over the target?

The answer is 5.71 seconds but i dont know how to get it?

Answer 1

X = Xo + Vot + 1/2at^2

160 = 0 + 0 =1/2(9.8)t^2      (9.8 is for gravity)

320 = 9.8t^2

32.65 = t^2

5.71 = t