So initially, we have zero of this, zero of this and 0.3
molar of our acid. We want to find the equilibrium concentration. So in equilibrium, our PH is 3.5. That means we could use the lock formula to find the concentration of this guy. Now, after we find the concentration of this guy, the concentration of this guy is the same thing. That's because 1 mol and 1 mol, our ratio of this guy to this guy is one to one.