The concentration of this guy increases by x, and the concentration of this guy decreases by x because this guy dissociates into this guy. So we get our hydronium concentration, we represent as x. Our pyruvate concentration we present as x because we begin with this concentration divide by since we begin with this amount of Peruvic acid and then some dissociates into the conjugate base, we say that it's 0.5 minus x. Now we approximate because the x is much smaller than 0.5 or 0.7 or 0.5. We approximate this to be 0.7. X divided by 0.5 equals our Ka.