Projectile and vectors?

Question

The pilot of an airplane traveling 180 km/h wants to fdop supplies to flood victims isolated on a ppatch of land 160m below. The supplies should be dropped 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

160-4.9x^2 = 0 @ 5.71is how long it takes to hit the ground