To determine the vertical velocity of the package after 20 seconds, we need to know the initial vertical velocity of the package and any acceleration acting on it. However, since only the horizontal speed of the moving plane is given (25 m/s), we assume that the package has no initial vertical velocity and there is no vertical acceleration acting on it (i.e., we neglect the effects of air resistance and gravity).
Under these assumptions, the vertical velocity of the package remains constant at zero throughout its motion. Therefore, after 20 seconds, the vertical velocity of the package is still 0 m/s.