 Okay. So this one's number one. This is just a dilution problem. If you're having problems with this, there's a couple more dilution problems on the website. So you can look at those videos as well. But this one's calculate the number of builds you would need to use to prepare a 5.0 liter of .2 molar NaOH from a 5.23 molar stock solution. So you need to know that you need to use the equation m1v1 equals m2v2 or mcvc equals mgvd. So this is concentration and diluted, concentrated and diluted, if you want to think of it that way. And then what I would do with these ones is just write down the variables. So the molarity of the concentrated is 5.23 molar. That's more concentrated. The volume of the concentrated is what we're looking for. The molarity of the dilute is 0.20 molar. And the volume of the dilute is 5.0 liters. So all you got to do in this one is isolate the vc variable. So you're just going to divide both sides by mc. Of course that will cancel that out. Given you this equation here, vc equals mgvd over mc. So md is 0.20 molar, vd divided by mc is 5.23 molar. Okay, notice molar and molar cancel out. And you're left with liters. So if we do this, we get 0.2 times 5 divided by liters, right? But it asks us at milliliters. Not to mention this is the right number of supers. So we're going to get milliliters out of this, 191 milliliters. Or since that's not the right number of supers, you could do 1.9 times 10 squared.