1. **State the problem:** We want to find the total cost of a dentist visit if the base price is 50 and there is an additional charge of 100 for each cavity filled. 2. **Formula:** The total cost $C$ can be expressed as $$C = 50 + 100n$$ where $n$ is the number of cavities. 3. **Explanation:** The base cost is 50 regardless of cavities. 4. For each cavity, an extra 100 is added, so multiply 100 by $n$. 5. Add the base cost and the additional cost to get the total. This expression correctly models the total cost of the visit based on the number of cavities filled.