The normal temperature is 73.5°F. Then, the animal is considered unhealthy if its temperature overcome the normal termperature.
Furthermore, if the temperature differs, at least 2.5°F, the animal can be considered as unhelathy.
You can write the previous statement by using an inequality as follow:
where x is the temperature of the animal. The previous expression stablishes that if the temperature x of the animal differs from the normal temperature (73.5), the animal can be considered as unhelathy.