The pilot of an airplane traveling 190 km/h wants to drop supplies to flood victims isolated on a patch of land 100 m below.

How many seconds before the plane is directly overhead should the supplies be dropped? ... ?

All we need to calculate is the time it takes for the supplies to fall from the plane to the ground. Using the free-falling body equation,

y = - 1/2*gt^2 + y00 = - 1/2*9.80*t^2 + 100t = 4.52 s.

The supplies should be dropped 4.52 s before the plane is directly overhead.