Okay, so for the first part, it's just subtraction. The stuff is lead and sulfur, so if the whole thing is 2.34 grams, and the lead part is 2.03 grams, we subtract the lead's mass from the whole and get 0.31 grams, the mass of the sulfur part.
For the second part, we take the sulfur's mass, 0.31 grams, and put it as the numerator (the top part) in a fraction, over the mass of the whole thing, 2.34 grams. This gives us an answer of .31/2.34 . My professor didn't ever use the term "Mass fraction" so if that's not what you were looking for, let me know.
For the third part, we have to convert the fraction to a decimal. To do this, we simply go ahead and divide the fraction, instead of leaving it. ( .31 divided by 2.34 ), and multiply our answer by a hundred. for instance, if we had 1/2, we divide 2 by 1 and .5, which we multiply by 100 giving us 50, and 50% is obviously 1/2. So, when we do this to the fraction .31/2.34 , we get 13.24, or around 13%.
So, our answers are:
(a) .31 grams
Calculate the mass of sulfur in the sampl ingalena lead