 So, let's finish up this unit with a couple of mass percent problems, and we'll do the mass percent of both of the atoms in carbon dioxide, and just show you how it's done. But anyway, so the first question asks, what is the mass percent of carbon in carbon dioxide? So of course, you're going to have to, well, it says C, and CO2. If you want to say it like that, you're going to have to know the names of both of those. But anyways, how do I do this problem? Well, I have to look at, I have to have a periodic table given to me, and I have to be able to know where to get the average atomic weight of carbon. So when I look at the periodic table, I'll get the average atomic weight to be in the periodic table I'm using, 12.011 AMU. So to do a percentage, you do the part divided by the whole times 100%. Well, this is the part you want, and this is the whole, but you don't know how much the whole thing weighs. So, and you're doing, trying to do mass percent, so you need to figure that out. So, you know how much part of it weighs, the carbon part, but you don't know how much the oxygen part weighs. So, you're going to also have to figure out, well, what's oxygen? So the average atomic mass of oxygen in the periodic table I'm using is 15.9994 AMU. Okay, and you've got to remember there's two of those oxygens, right? So, you're going to have to multiply this by two. Okay, so let's do that. Let's figure out what the molecular weight of the carbon amount is. So, 15.9994 times two plus 12.011. Okay, so I get this number, 44.8. Okay, so in order to do mass percent, like we said, we do the part for the whole. In this case, the mass of carbon gives me, well, how many sick things am I going to want to? Next, we'll do a percentage of oxygen.