So this guy becomes a negative. And now notice we have a plus C and a minus C. So the C's cancel and we get just this guy plus this guy. And that's exactly what we have right here. Now our next step is to basically equate this guy, to simply this guy and rewrite the equations to a better looking formula so this guy, using the logs of logs, we can rewrite in this format. So natural log of P final divided by P initial equals. Now, notice on this side, we have two common terms or one common term.