1. **State the problem:** Savannah has 400 chocolate chips. She saves $x$ chips for garnish and divides the remaining chips evenly into 3 pans of brownies. 2. **Formula used:** To find the number of chips in each pan, subtract the saved chips from the total and then divide by 3. 3. **Expression:** $$\frac{400 - x}{3}$$ 4. **Explanation:** We first calculate how many chips are left after saving $x$ chips, which is $400 - x$. 5. Then, since the remaining chips are divided evenly into 3 pans, we divide by 3. 6. **Final answer:** Each pan contains $$\frac{400 - x}{3}$$ chocolate chips.