Apackage rests on the floor of an elevator that is rising with constant speed. the elevator exerts an upward normal force on the package, and hence does positive work on it. why doesn't the kinetic energy of the package increase?

Because the actual package isn't moving so the gravitational potential energy stays the same. kinetic energy is gained through motion of the object not the motion of the surroundings of the object so
unless the package is falling out of a window its losing gravitational potential energy and gaining kinetic energy. hope this helps :-) 

The masses of the objects and their densities