That's a very small amount. So now we have this very simple situation in which we simply bring over the 0.2, multiply it by 1.8
times ten to negative five equals X squared. Take the radical, and we get 1.8 times ten to negative five times zero. Two radical gives you two answers a positive and a negative. We reject the negative because concentrations can't be negative and we take the positive guy. Now look how close this guy is to this guy.