 Okay, wonderful. So let's try this one. It says, find the concentration of calcium in parts per million in a 3.50 gram pill that contains 40.5 milligrams of calcium. So this question is a mass by mass problem, okay? But remember, mass, mass percent problems, we did mass divided by mass times 100%. This one's a part per million problem, okay? So instead of per cent, which everybody understands, cent means 100, if you didn't know that, you know it now, okay? So parts per million, what are we going to multiply by? To the 6 or a million, right? Yeah, okay? So the first thing we're going to have to do, though, is get these two units in the same unit. So if you prefer to take this to milligram or this one to grams, I'll take this one to grams, it's just preferable to me. So that's going to be 0.0405 grams of calcium, right? Calcium at 3.50 grams altogether total in the pill, right? So how do I do the PPM? Just like what we said, it's going to be the mass of, well, in this case, calcium, divided by the mass of the pill. Make sure they're in the same unit times, well, a million, in terms of the 6, okay? Everybody okay with doing this? So what do I get? 0.0405 grams. Make sure you keep your units there. Divided by 3.50 grams, okay? Times 10 to the 6, cancel, cancel, like that. What are my units? Well, this is 10 to the 6, sorry, this is PPM. Now what are my units? Sorry, PPM. Okay, so let's just plug these guys in. So 0.0405 divided by 3.5 times 10 to the 6. And how many sig figs are we going to add here? 3, 1.16 times 10 to the 4, right? 1, 2, 4. PPM of calcium in the pill. So let's go on upstairs and continue along with this discussion.