 Okay, so this problem is asking us whether these results are consistent with the law of conservation of mass. So the law of conservation of mass states that if the two substances completely react, then the mass of one side of the reaction will be equivalent to the mass of the other side of the reaction. So hopefully you can see in the first reaction we have hydrogen gas and oxygen gas as our reactants, and if we add up the total mass of those two reactants we get 67.5 grams. And then we go over to the products and we see waters are our only product in that reaction, and it is also 67.5 grams. So since 67.5 grams equals 67.5 grams, we can say that that example has been consistent with the law of conservation of mass. On the other hand, when we look at the next example, this one is not consistent because it says that gasoline here is completely reacting with oxygen, the 60.5 grams of gasoline with the 243 grams of oxygen to give us only 206 grams of carbon dioxide and 88 grams of water. So what that means is when we add those up we get 303.5 grams or 304 grams with significant figures on the left hand side of that reaction and 294 grams on the right hand side. Those two reactants had reacted completely, then we wouldn't have the 10 grams of lost mass left over. So if you add those two up there's a 10 gram difference between them. So that is not consistent, B is not consistent with the law of conservation of mass. Okay, thank you.