Light escaping a glass cube with central spot: which faces to cover?

[Electro]

Hello to all,
I have a physics problem regarding reflection of light.

A solid glass cube, of edge 10 mm and n = 1.5 has a small spot at its center. a) What parts of each cube face must be covered to prevent the spot from being seen, no matter what the direction of viewing? b) What fraction of the cube surface must be covered?

The point is that I don't get what the problem is implying. Anyone can give a hint or just a startup clue?
Thank You

 

[Source]

When viewed from certain angles, the spot would not be visible due to bending (refraction) of light; however, the spot would be visible at certain other points. It's asking what must be 'blacked out,' so to speak, in order for the spot never to be seen from the areas where refraction wouldn't prevent it from being seen, and then, what fraction (how much) of the surface area must be covered.