Answer is: the ramp's mechanical advantage increases because friction has been reduced. Friction is the force resisting the relative motion. Lubrication is the process that reduce friction between surfaces in moving to each other. Grease is a liquid-liquid dispersion that possess a high viscosity and allows smooth continuous operation of equipment.
if we applying grease on the ramp, it would be very smooth and the frictional force acting against the box sliding will be decreased. so, it would be quite easy to slide the box on the ramp with very less effort.
