So let's rearrange them a bit and we get well, we bring that change in concentration of x over this side and we bring our time or change in time to this side. We also bring the negative over to this side and we get change in concentration of x divided by concentration of x equals negative our constant times change in time. Now, in order to get from this guy to this guy, we have to use calculus and integrals. Now I will spare you the calculus and we'll simply jump to this step. If you're interested about what to do from this step to this step, leave a comment and I'll show you. So after we use calculus, we get natural log of the concentration of final minus natural log of concentration of initial equals negative k times time final minus time initial.