So we replace this quantity with the right side of this equation, and we get equation three. So the change in entropy of our system is minus the change in entropy of the system divided by the temperature, which is the same thing as the change in entropy of our surroundings is equal to the change in entropy of our universe. Let's call this equation three. Now, if we take equation three and multiply each term by negative T, we get this equation here. So this becomes negative T, delta S system. This becomes positive delta H system.