If the mask is open and not sealed in plastic, no one will want it.
As to the machine - you need to provide more information - include everything you can find written on the top - and the model number you should find on the bottom
once we know the unit, someone can tell you how to determine how many hours are on it.
But be prepared, unless the unit is very new - not a discontinued unit - there won't be a lot of interest in people purchasing it.
However there are places where you can donate it for people who lack insurance and can't afford to buy new