if a student places a finger and pushes with 75 newtons of force straight down but the pencil doesn't move,how much work is done? why?
Work, by definition, is the product of the force and the displacement (in the direction of the displacement).
In our case the displacement is zero, so its product with anything is also zero. The answer is 0.
The sense is that not only efforts must be made but also some results should be achieved.