Mass Percent, atom percent, mass fraction, elemental fraction

To do any mass percent question one must first understand a little about fractions.  If one has a fruit basket, with 3 apples, 2 oranges, 4 bananas, and a grapefruit, we could say that there is %30 apples in the basket, %20 oranges and so on if we were talking about the percentage by fruit.  

If we were talking about percentage by mass we would need to know the masses of the individual fruits, as well as the total mass (which we could get from the former).  

This is the same thing when we talk about molecules, or chemical compunds.  The question was not given, but I will give an example that you can hopefully follow....