I'm always impressed at the lack of basic math and reading comprehension skills...

The FHR site says the free night is included in the nightly rates. That means that the rate they display is the rate per night you're staying, including the night that you are staying for 'free'. Typically you'd expect the '4th night free' rate to be (rate*.75) but, as geoffk points out, the non-discounted rate on the FHR site isn't always the base rate upon which the 4th night discount is based.

In short, if the site says you get a night free that's included in the rate, then just consider the posted rate as the nightly cost for every night of your trip.