That means this guy, the x will go to zero. So let's rearrange this a bit. Let's bring the negative over here. Let's bring the T on this side and make this guy one because 80 power is one and we get change in concentration of x equals negative constant k times change in time. Now let's represent this guy and this guy following way. So the final concentration minus the initial concentration equals negative k in parentheses time final minus time initial.