Answer
The plane should drop the package 678 meters short of the target.
Work Step by Step
We can find the time for the package to drop 100 meters as:
$y = \frac{1}{2}gt^2$
$t = \sqrt{\frac{2y}{g}}$
$t = \sqrt{\frac{(2)(100~m)}{9.80~m/s^2}}$
$t = 4.52~s$
The we can find the horizontal distance that the package will travel in 4.52 seconds:
$x = v_x~t = (150~m/s)(4.52~s)$
$x = 678~m$
The plane should drop the package 678 meters short of the target.
