 Okay, so this, like I was just saying, this is the same type of problem that we've been doing, but the only thing you need to do is balance the equation first and then do that analysis that we've been doing. So metallic iron, we've got to know that that's epi-solve plus, well, it reacts with O2 gas to produce iron-3 oxide. The first thing we need to do is balance this equation. Okay, so we've got two oxygens here and two oxygens here. So what we're going to do is try to find a common multiple of those two numbers, okay? And that's going to be six. So we're going to put two there because three times two, three times two is six. We're going to put three there, okay? Because two times three is six. Next, so now we've got six oxygens here, six oxygens there. How many irons do we have here? Four, all right? We only have one here, so we're going to put a four there. So now we need to calculate the mass of iron needed to produce five grams of product, okay? So we know the mass of iron-3 oxide is 5.0 of grams. Also, iron-3 oxide is what we need to get down, moles here and grams there. That's going to be the molar mass. It's going to be one mole, but we need to figure out what the molar mass is here. So Fe is 55 and 85. We'll do two times that because we've got that there. Oxygen is going to be three times 16.00. And if I had enough room, I would put grams per mole on both of these. Okay, so let's figure out 0.5 equals 159.7. So if we take 5 divided by 159.7, we get 0.0313 moles. So that's how many moles of iron-3 oxide we have. We're trying to figure out the mass of iron we need. So we have a 2 to 4 ratio, or a 1 to 2 ratio. So in order to find the number of moles of iron, all we have to do is take the number of moles of iron oxide, 0.0313 oxide, multiply it by 4 moles of iron, because it's a 2 to 4 ratio. Moles of iron-3 oxide can't allow. We take that, multiply it by 4, divide it by 2. We get 0.0626 moles of iron. And from there, just follow us to find the mass of iron. 0.0626 moles of FV. We want to take the moles of FV out. So for every one mole of FV, we've got 55.85 grams of iron. Moles of iron cancel. So we just take 0.0626 and multiply it by 55.85. 3.50 grams of iron. So 3.50 grams of iron is needed to produce 5 grams of profit.