The kit has position vector with components
[tex]x=\left(140.0\,\dfrac{\mathrm m}{\mathrm s}\right)t[/tex]
[tex]y=1800.0\,\mathrm m-\dfrac g2t^2[/tex]
It would take time [tex]t[/tex] for the kit to reach the ground from freefall:
[tex]0=1800.0\,\mathrm m-\dfrac g2t^2\implies t=19.2\,\mathrm s[/tex]
It sounds like Alex's plane is 1800 m above the ground, at some (horizontal) distance away from the explorers below, and is heading in their direction. In order to have the kit drop down where the explorers are located, Alex should release the kit at a distance of
[tex]x=\left(140.0\,\dfrac{\mathrm m}{\mathrm s}\right)(19.2\,\mathrm s)\approx2690\,\mathrm m[/tex]
away from the explorers.
