Finding the formula

 is a note which can be found inside the Nuka-Cola Plant in Fallout 3. Upstairs in the office section, near the shipping section, you should find the body of Winger Mercier. When you search him, you will find this note. Examining the note via your Pip-Boy 3000 will trigger the quest Just for the Taste of It.

The note calls for Winger Mercier to find the secret Nuka-Cola Clear Recipe from the R&D Department of the Nuka-Cola Plant and return it to his partner, Goalie Ledoux, who is awaiting him at the Red Racer Factory.