Nicola takes a moment to study the ghosts. He is trying to think up a new method to determine just how old these ghosts are. He knows that their age is somehow related to their opacity. To measure their opacity Nikola uses a scale of 10000 units to 0 units, where 10000 is a completely opaque newborn ghost (0 years old) and 0 is completely transparent ghost (of an unknown age).
After some experimenting, Nikola thinks he has discovered the law of ghostly opacity. ...) or increased by 1 if it is not.